| - | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
| Athlete | Sex | First Appearance | Last Appearance | Appearances | Colleges | Race Types |
|---|---|---|---|---|---|---|
| Eanna O Bradaigh | m | 2024-03-09 | 2024-04-06 | 3 | UCD | 5000m, XC |
| Jared O Briain | m | 2023-11-10 | 2023-11-10 | 1 | UG | Road |
| Daniel O Brien | m | 2021-11-13 | 2024-04-06 | 17 | MU | 10000m, 1500m, 3000m, Road, XC |
| Mark O Brien | m | 2023-04-21 | 2023-04-22 | 2 | MTU | 1500m, 800m |
| Cormac Ó ceallaigh | m | 2018-11-17 | 2019-11-16 | 6 | IT Carlow | 1500m, 3000mSC, Road |
| M. Ó Ceallaigh | m | 1961-05-14 | 1961-05-14 | 1 | NACA | DT |
| Mark O Connor | m | 2022-11-11 | 2024-04-06 | 15 | GST, MTU | 1500m, 3000mW, 400m, 400mH, 4x200m, 4x400m, 800m, Road, XC |
| Peter O Connor | m | 2017-02-10 | 2017-05-27 | 8 | IT Carlow, IUAA | 110mH, CE, JT, LJ, SP |
| Jack O Donnell | m | 2023-11-10 | 2024-04-06 | 8 | TUS | 800m, Mixed 4x400m, Road |
| Andrew Ó Donnghaile | m | 2016-03-05 | 2019-03-02 | 11 | UG | 10000m, 3000m, 3000mSC, 5000m, Road, XC |
| Andrew Ó Donnghaile | m | 2022-03-05 | 2022-03-05 | 1 | UG | XC |
| Alan O Donovan | m | 2018-11-17 | 2019-02-08 | 3 | CIT | 800m, Road |
| Conor O Driscoll | m | 2018-04-13 | 2018-04-14 | 3 | UCC | 4x400m, 800m |
| Adam O Dwyer | m | 2022-01-29 | 2022-04-09 | 2 | CIT | PV |
| Maritin O Goibin | m | 2023-11-10 | 2024-04-06 | 5 | TUD | 3000m, 5000m, Road |
| Ruadhán Ó gráda | m | 2018-03-10 | 2019-11-16 | 5 | UCD | 1500m, Road, XC |
| Fionn O Hanluain | m | 2023-11-10 | 2024-04-06 | 4 | ATU | 400m, LJ, Road |
| Risteard Ó Hannracháín | m | 2009-11-14 | 2011-03-12 | 3 | TCD | Road, XC |
| Ailin O Harrachtain | m | 2024-02-10 | 2024-02-10 | 2 | MTU | 1500m |
| S. Ó Laithimh | m | 1934-05-26 | 1934-05-26 | 3 | UCG | 440y, 880y, Mile |
| Ruadhan O Laoi | m | 2013-03-09 | 2013-03-09 | 1 | RCSI | XC |
| Daniel O Mahony | m | 2016-11-19 | 2018-04-14 | 12 | CIT | 400m, 400mH, 4x200m, 4x400m, Road |
| Josh O Mahony | m | 2022-11-11 | 2024-04-06 | 6 | GST, MTU | 400m, Mixed 4x400m, Road |
| Aogán Ó Muircheartaigh | m | 1967-05-05 | 1968-05-01 | 10 | UCD | 100y, 120yH, 220y, 4x110y |
| Colm A. Ó Muircheartaigh | m | 1965-05-08 | 1966-05-18 | 10 | IUAA, UCD | 220y, 440y, 440yH, 4x110y |
| Iognáid G. "Iggy" Ó Muircheartaigh | m | 1961-06-01 | 1967-05-27 | 34 | BLE, IUAA, NACA, UCD | 100y, 220y, 440y, 4x110y |
| Seán F. Ó Muircheartaigh | m | 1964-05-20 | 1969-07-12 | 41 | IUAA, UCD | 120yH, 440y, 440yH, 4x110y, LJ, TJ |
| Cóil Ó Muirí | m | 2023-11-28 | 2023-11-28 | 1 | DCU | SP |
| Coil O Muiri | m | 2024-02-10 | 2024-04-06 | 2 | DCU | 35lbWfD, HT |
| Connor O Neill | m | 2021-11-13 | 2022-04-09 | 5 | CIT | 4x400m, 800m, Road, XC |
| Connor O Neill | m | 2023-04-21 | 2024-04-06 | 4 | MTU | 4x400m, Mixed 4x400m |
| Danny O Neill | m | 2017-02-10 | 2017-02-10 | 1 | CIT | 60m |
| James O Neill | m | 2017-05-27 | 2017-05-27 | 1 | GST | DT |
| Tomas O Neill | m | 2017-04-07 | 2017-04-08 | 2 | IT Tralee | DT, HT |
| Eoin O Reilly | m | 2024-04-05 | 2024-04-06 | 1 | MTU | 3000mSC |
| Breandán Ó Riain | m | 2012-04-20 | 2012-04-21 | 2 | UCD | HJ, LJ |
| Shane O Riordan | m | 2016-11-19 | 2017-03-04 | 4 | WIT | 3000m, Road, XC |
| Stephen O Shea | m | 2022-11-11 | 2024-04-06 | 6 | GST, MTU | 3000mW, 800m, Mixed 4x400m, Road |
| Luke O' Carroll | m | 2022-01-29 | 2024-04-06 | 20 | UL | 100m, 4x100m, 4x200m, 60m, LJ, SP, TJ |
| Ben O' Connell | m | 2022-11-11 | 2023-04-22 | 5 | UCC | 400m, 4x200m, 4x400m, Road |
| Sean O' Connell | m | 2021-11-13 | 2023-04-22 | 4 | UCC | 10000m, Road, XC |
| Darragh O' Leary | m | 2021-09-26 | 2024-04-06 | 10 | UL | 3000mSC, 5000m, Mile, Road, XC |
| Jack O' Leary | m | 2022-01-29 | 2022-01-29 | 3 | IT Tralee | 1500m, 800m |
| Daire O' Sullivan | m | 2022-01-29 | 2022-04-09 | 5 | UL | 1500m, XC |
| Michael J. O'B. Kennedy | m | 1972-05-05 | 1974-05-04 | 6 | TCD | 110mH, 400mH, PV, TJ |
| S. O'Bearain | m | 1946-07-14 | 1947-05-21 | 2 | UCD | DT |
| B. O'Beirne | m | 1952-05-22 | 1952-05-22 | 1 | UCD | HJ |
| J. O'Beirne | m | 1976-05-11 | 1976-05-11 | 1 | UCD | DT |
| S. O'Bioram | m | 1949-05-26 | 1949-05-26 | 1 | UCD | DT |
| Cian O'Boyle | m | 2024-03-09 | 2024-04-06 | 3 | UL | 4x400m, 800m, XC |
| Malcom O'Boyle | m | 2023-11-10 | 2024-02-10 | 2 | TUD | 800m, Road |
| Neal O'Boyle | m | 1968-11-30 | 1971-02-20 | 6 | UCD | XC |
| S. O'Boyle | m | 1988-03-05 | 1988-03-05 | 1 | UU | XC |
| Eanna O'Bradaigh | m | 2021-11-13 | 2023-11-10 | 2 | TCD, UCD | Road |
| Ruairi O'Briain | m | 2001-12-07 | 2010-04-24 | 23 | IUAA, UCD | 4x100m, HJ, LJ, PV, TJ |
| Paddy O'Brian | m | 2007-11-17 | 2007-11-17 | 1 | WIT | Road |
| D. O'Bric | m | 1970-05-09 | 1972-05-06 | 2 | SPM | 200m |
| A. O'Brien | m | 1989-05-05 | 1989-05-06 | 1 | UCD | 400mH |
| Aaron O'Brien | m | 2013-11-23 | 2014-04-12 | 3 | UL | 3000m, 5000m, Road |
| Adam O'Brien | m | 2017-03-04 | 2018-04-14 | 6 | DCU, IUAA | 10000m, 5000m, Road, XC |
| Alan O'Brien | m | 2011-03-12 | 2016-04-16 | 7 | CIT | 400mH, Road, XC |
| Andrew O'Brien | m | 2015-11-14 | 2019-11-16 | 18 | MU | 10000m, 1500m, 200m, 3000m, 400m, Road, XC |
| B. O'Brien | m | 1934-05-26 | 1934-05-26 | 1 | UCC | LJ |
| Barry O'Brien | m | 2000-12-01 | 2000-12-02 | 3 | NUIM | 200m, 60m, 800m |
| Brendan O'Brien | m | 1997-12-12 | 1998-02-28 | 2 | DCU | 1500m, XC |
| Brian O'Brien | m | 1938-05-26 | 1939-05-27 | 8 | UCG | 100y, 220y, LJ, SP |
| Carwin O'Brien | m | 2003-11-22 | 2003-11-22 | 1 | UCC | Road |
| Cathal O'Brien | m | 2015-04-10 | 2015-04-11 | 1 | DCU | HJ |
| Cian O'Brien | m | 2018-02-09 | 2019-02-08 | 4 | Ireland, WIT | HJ |
| Ciaran O'Brien | m | 2000-04-14 | 2002-04-20 | 10 | WIT | 100m, 200m, 4x100m, 4x200m, 60m, 800m |
| D. O'Brien | m | 1980-05-02 | 1980-05-03 | 1 | UCD | HJ |
| D. O'Brien | m | 1989-05-05 | 1989-05-06 | 1 | UCD | 400mH |
| Daniel P. "Dan" O'Brien | m | 1935-05-25 | 1939-05-27 | 13 | UCD | 120yH, LJ, SP |
| Danny O'Brien | m | 1989-05-05 | 1992-04-25 | 10 | NIHEL, UL | 400m, 800m, XC |
| Danny O'Brien | m | 2023-11-10 | 2023-11-10 | 1 | DCU | Road |
| Darren O'Brien | m | 1999-04-23 | 2004-04-17 | 15 | UCC | 100m, 200m, 400m, 4x100m, 4x200m, 4x400m, 60m |
| David O'Brien | m | 2012-04-20 | 2014-04-12 | 12 | CIT | CE, HJ, LJ, SP |
| Derek O'Brien | m | 1999-04-23 | 1999-12-04 | 6 | IT Carlow | 100m, 200m, 4x100m, 60m, LJ |
| Diarmuid O'Brien | m | 2012-03-10 | 2013-03-09 | 5 | RCSI | 1500m, Road, XC |
| Dylan O'Brien | m | 2017-02-10 | 2017-04-08 | 4 | TGC | 3000m, 5000m, XC |
| Dylan O'Brien | m | 2023-03-04 | 2023-03-04 | 1 | NCI | XC |
| E. O'Brien | m | 1994-02-19 | 1994-02-19 | 1 | TCD | XC |
| Eamonn O'Brien | m | 1989-05-05 | 2011-02-05 | 7 | UCD | HJ, TJ |
| Emmet O'Brien | m | 2013-02-01 | 2013-02-01 | 1 | DKIT | 800m |
| Fergus O'Brien | m | 1982-04-30 | 1984-05-05 | 7 | TCD | DT, HT, SP |
| Fergus O'Brien | m | 2023-11-10 | 2024-03-09 | 3 | UL | Mile, Road, XC |
| G.D. O'Brien | m | 1952-05-22 | 1952-05-22 | 1 | UCG | Mile |
| Hugh O'Brien | m | 2023-01-28 | 2023-04-22 | 3 | UCD | HJ, LJ |
| J. O'Brien | m | 1979-05-23 | 1979-05-23 | 1 | UCD | LJ |
| J. O'Brien | m | 1964-05-30 | 1964-05-30 | 1 | AAUE | 120yH |
| J.S. O'Brien | m | 1922-06-10 | 1924-05-31 | 3 | UCD | SP |
| Jake O'Brien | m | 2023-11-10 | 2024-04-06 | 3 | UL | 2000mW, 3000mW, Road |
| John O'Brien | m | 2003-03-09 | 2003-03-09 | 1 | IT Tralee | XC |
| John O'Brien | m | 2003-04-25 | 2003-04-26 | 3 | IT Carlow | 100m, 200m, LJ |
| John Paul O'Brien | m | 1997-12-12 | 2003-04-26 | 14 | UL | 1500m, 3000m, 800m, Road, XC |
| John Paul O'Brien | m | 2000-02-26 | 2002-12-07 | 22 | UG, UL | 110mH, 400mH, 4x100m, 4x200m, 4x400m, 60mH, CE, HJ, LJ, PV, SP, XC |
| Justin O'Brien | m | 1985-05-03 | 1985-05-04 | 1 | RCSI | PV |
| Kevin O'Brien | m | 2005-11-19 | 2006-11-18 | 3 | UL | Road, XC |
| L. O'Brien | m | 1914-06-06 | 1914-06-06 | 1 | TCD | 880y |
| L. O'Brien | m | 1975-03-08 | 1977-03-12 | 3 | NCPE | XC |
| Liam O'Brien | m | 1978-06-30 | 1978-06-30 | 1 | President's Select | 3000mSC |
| Liam O'Brien | m | 1994-02-19 | 1994-02-19 | 1 | Cork RTC | XC |
| Liam O'Brien | m | 2004-02-06 | 2010-04-24 | 36 | CIT | 100m, 200m, 400m, 4x100m, 4x200m, 4x400m, 60m, SP |
| Liam O'Brien | m | 1999-12-03 | 1999-12-04 | 3 | WIT | 200m, 4x200m, 60m |
| Liam O'Brien | m | 1974-05-03 | 1977-06-14 | 6 | BLE Select, NCPE | 1500m, 3000mSC |
| Luke O'Brien | m | 2018-04-13 | 2018-04-14 | 1 | MU | JT |
| M. O'Brien | m | 1938-05-26 | 1938-05-26 | 1 | UCC | 100y |
| M. O'Brien | m | 1982-03-06 | 1982-03-06 | 1 | UCC | XC |
| Michael O'Brien | m | 1987-05-08 | 1991-05-04 | 8 | UCC | DT, HT, SP |
| Michael "Mick" O'Brien | m | 1988-04-29 | 1988-04-30 | 2 | UCD | 110mH, 400mH |
| Myles O'Brien | m | 2001-11-07 | 2001-11-07 | 2 | UCC | Road |
| Nathan O'Brien | m | 2004-12-03 | 2007-04-14 | 10 | UL | 200m, 400m, 4x100m, 4x200m |
| Oran O'Brien | m | 2022-01-29 | 2022-04-09 | 5 | DCU | 35lbWfD, DT, SP |
| P. O'Brien | m | 1970-05-09 | 1970-05-09 | 2 | SPM | DT, SP |
| P. O'Brien | m | 1978-03-04 | 1978-03-04 | 1 | TCD | XC |
| P. O'Brien | m | 1988-03-05 | 1989-05-06 | 4 | NIHED | 5000m, XC |
| P. O'Brien | m | 1983-05-06 | 1983-05-07 | 1 | UCD | 200m |
| Paul O'Brien | m | 1982-05-12 | 1982-05-12 | 2 | UCD | 100m, 200m |
| Paul O'Brien | m | 2012-03-10 | 2012-03-10 | 1 | CIT | XC |
| Peter O'Brien | m | 2015-02-06 | 2015-05-31 | 3 | DIT, IUAA | PV |
| R. O'Brien | m | 1975-03-08 | 1975-03-08 | 1 | UCC | XC |
| Russell O'Brien | m | 1970-05-09 | 1970-05-09 | 1 | UCC | 400m |
| Russell O'Brien | m | 1967-05-05 | 1971-05-08 | 7 | UCC | 4x100m, 800m, 880y, XC |
| S. O'Brien | m | 1967-06-01 | 1968-05-11 | 3 | UCD | 120yH, LJ, PV |
| T. O'Brien | m | 1974-05-03 | 1974-05-15 | 2 | UCD | 4x100m |
| T.P. O'Brien | m | 1930-06-07 | 1934-05-26 | 8 | IUAA, UCC | 880y, 880y, 220yx2, 440y, Mile |
| Ted O'Brien | m | 1993-04-23 | 1995-06-17 | 16 | IUAA, UL | CE, DT, HJ, PV, SP, TJ |
| Terry O'Brien | m | 2002-04-19 | 2002-04-20 | 2 | CIT | DT, SP |
| Thomas O'Brien | m | 2000-04-14 | 2000-12-02 | 4 | DCU | 100m, 200m, 60m |
| Vivion C. "Viv" O'Brien | m | 1974-05-03 | 1980-05-14 | 25 | TCD, UCD | 100m, 200m, 4x100m, LJ |
| A. O'Brien-Moran | m | 1939-05-27 | 1939-05-27 | 1 | UCD | DT |
| Timothy O'Brien-Pifer | m | 2024-03-09 | 2024-03-09 | 1 | UCD | XC |
| Cpl. M. O'Byrne | m | 1961-05-14 | 1961-05-14 | 1 | Army | Mile |
| Iain O'Byrne | m | 2009-03-07 | 2010-03-13 | 4 | WIT | 3000mSC, Road, XC |
| Iain O'Byrne | m | 2018-02-09 | 2018-02-09 | 2 | TGC | 1500m |
| Jason O'Byrne | m | 2008-03-08 | 2010-11-13 | 6 | DCU | 3000mSC, 3000mW, Road, XC |
| Myles O'Byrne | m | 2001-12-07 | 2002-04-20 | 4 | UCC | 1500m, 5000m, XC |
| N. O'Byrne | m | 1989-05-05 | 1989-05-06 | 1 | NIHED | 800m |
| Tom O'Byrne | m | 2000-04-14 | 2002-04-20 | 6 | CIT | 100m, 200m, 4x400m, 60m |
| Tomas O'Byrne | m | 2006-11-18 | 2006-11-18 | 1 | CIT | Road |
| Alan O'Cais | m | 2004-11-20 | 2005-11-19 | 2 | TCD | Road |
| Aidan O'Callaghan | m | 1994-01-21 | 1998-06-23 | 13 | IUAA, Queen's Select, UCD | 10000m, 3000m, 3000mSC, 5000m, XC |
| Aidan O'Callaghan | m | 1997-02-16 | 1997-02-16 | 1 | GST | XC |
| Aidan O'Callaghan | m | 1997-02-01 | 1998-04-25 | 4 | UCC | 10000m, 3000mSC, XC |
| Aidan O'Callaghan | m | 2010-03-13 | 2012-02-04 | 6 | TCD | 200m, 4x200m, 60m, XC |
| Brian O'Callaghan | m | 1959-05-13 | 1962-05-17 | 5 | UCC | 100y, DT, SP |
| Caolan O'Callaghan | m | 2017-02-10 | 2020-02-15 | 14 | GST, Ireland, UL | HJ, LJ, TJ |
| Conall O'Callaghan | m | 2012-02-04 | 2012-02-04 | 5 | UCC | 200m, 4x200m, 60m |
| D.J. O'Callaghan | m | 1921-06-04 | 1924-05-31 | 2 | UCC | 220y |
| Darragh O'Callaghan | m | 2010-11-13 | 2010-11-13 | 1 | UCC | Road |
| David O'Callaghan | m | 1993-03-06 | 1993-03-06 | 1 | UCC | XC |
| David O'Callaghan | m | 2006-04-21 | 2006-04-22 | 1 | UU | HJ |
| Dr Patrick "Pat" J. O'Callaghan | m | 1929-06-01 | 1931-05-30 | 18 | IUAA, UCC | 120yH, DT, HJ, HT, LJ, SP |
| Fegal O'Callaghan | m | 2018-11-17 | 2018-11-17 | 1 | MU | Road |
| Fergal O'Callaghan | m | 1996-12-13 | 1998-02-28 | 6 | UL | 400m, 400mH, 800m, XC |
| Fergal O'Callaghan | m | 1993-02-12 | 1993-02-12 | 1 | UCC | HJ |
| Hugh O'Callaghan | m | 1961-05-14 | 1964-05-09 | 8 | IUAA, UCC | DT, JTo, SP |
| Hugh Dominic O'Callaghan | m | 1961-06-01 | 1964-05-31 | 8 | IUAA, TCD | 4x110y, DT, JT, SP |
| John O'Callaghan | m | 2002-12-06 | 2004-02-07 | 8 | IT Tralee | 1500m, 400m, 4x200m, 5000m, XC |
| Matthew Q. O'Callaghan | m | 1873-05-19 | 1873-05-19 | 4 | UCG | 2 Miles, 880y, Mile, PV |
| Mel O'Callaghan | m | 2016-02-12 | 2019-04-06 | 24 | WIT | 100m, 200m, 4x100m, 4x200m, 4x400m, 60m |
| Padraig O'Callaghan | m | 2020-02-15 | 2023-11-28 | 11 | UCC, UL | 35lbWfD, HT, SP |
| Padraig O'Callaghan | m | 2024-02-10 | 2024-04-06 | 6 | UL | 35lbWfD, DT, HT, SP |
| Pat O'Callaghan | m | 1977-06-14 | 1977-06-14 | 1 | BLE Select | 3000mSC |
| Pat O'Callaghan | m | 1954-05-22 | 1958-07-28 | 12 | IUAA, UCC | DT, SP |
| Paul O'Callaghan | m | 1999-04-23 | 1999-04-24 | 1 | UCD | 400m |
| Paul O'Callaghan | m | 2019-02-08 | 2020-02-15 | 6 | TCD | 400m, 4x200m, 4x400m |
| Pierce O'Callaghan | m | 1994-04-22 | 1998-04-25 | 8 | IUAA, UCD | 2000mW, 3000mW |
| Sean O'Callaghan | m | 2017-02-10 | 2018-04-14 | 17 | IUAA, UCC | 400m, 4x100m, 4x200m, 4x400m |
| Terrence "Terry" O'Callaghan | m | 1957-05-18 | 1959-05-13 | 7 | IUAA, UCC | DT, JTo, PV |
| Paul O'Callahan | m | 1999-03-06 | 1999-03-06 | 1 | UCD | XC |
| Frank O'Carrol | m | 2009-04-24 | 2011-11-12 | 7 | CIT | 10000m, 5000m, JT, Road, XC |
| Colum O'Carroll | m | 2022-01-29 | 2022-04-09 | 3 | WIT | 200m, 400m |
| Darragh O'Carroll | m | 2008-11-15 | 2009-02-15 | 3 | UCC | 12, 4, 8, 16, 400m, Road |
| Desmond Anthony O'Carroll | m | 1978-05-05 | 1979-05-23 | 6 | TCD | 100m, 200m, LJ |
| Edward O'Carroll | m | 2015-02-06 | 2015-02-06 | 2 | IADT | 4x200m |
| Eoin O'Carroll | m | 2016-04-15 | 2019-04-06 | 5 | UL | 4x100m, 60m, LJ |
| Liam O'Carroll | m | 1960-05-14 | 1962-06-06 | 5 | IUAA, UCD | PV |
| Louis O'Carroll | m | 2014-11-15 | 2016-11-19 | 5 | WIT | Road, XC |
| Louis O'Carroll | m | 2021-11-13 | 2022-03-05 | 2 | RCSI | Road, XC |
| Oisín O'Carroll | m | 2009-11-14 | 2012-04-21 | 9 | UG | 1500m, 4x100m, Road, XC |
| Ciarain O'Cathain | m | 2015-02-06 | 2015-02-06 | 1 | DCU | 60mH |
| Ciaran O'Cathain | m | 2007-12-08 | 2013-02-01 | 14 | DCU | 100m, 110mH, 200m, 4x100m, 4x200m, 60m, 60mH |
| Lorcan O'Cathain | m | 2010-04-23 | 2010-04-24 | 2 | GST | 200m |
| Feilibh O'Cinneide | m | 2010-02-13 | 2010-04-24 | 3 | ITB | 200m, 400m |
| Ruairi O'Cinneide | m | 2014-11-15 | 2020-02-15 | 12 | UCC, UCD | 2000mW, 3000mW, Road, XC |
| A. O'Cleirigh | m | 1981-03-07 | 1981-03-07 | 1 | UCG | XC |
| Cormac O'Cleirigh | m | 1950-05-17 | 1950-05-17 | 2 | UCD | 440y, 880y, 220yx2, 440y |
| Sean O'Cleirigh | m | 1950-05-17 | 1955-05-19 | 6 | UCD | 880y |
| Henry Dermot O'Clery | m | 1961-06-01 | 1961-06-01 | 2 | TCD | Mile, TJ |
| William O'Coill | m | 2004-11-20 | 2005-04-23 | 4 | TCD | 100m, 4x100m, HJ, Road |
| Eoin Pol O'Colgain | m | 2004-02-28 | 2005-02-26 | 2 | TCD | XC |
| Micheal Ó'Conaire | m | 1998-12-11 | 1998-12-12 | 1 | UG | 60m |
| Donnie O'Conchola | m | 1995-03-04 | 1995-03-04 | 1 | UCG | XC |
| Donnacha O'Conghaile | m | 1996-02-09 | 1996-02-10 | 1 | UCG | LJ |
| Micheal Ó'Connaire | m | 1998-12-11 | 1998-12-12 | 1 | UG | SP |
| B. O'Connell | m | 1989-03-04 | 1989-03-04 | 1 | UCC | XC |
| Christian O'Connell | m | 2018-04-13 | 2019-04-06 | 2 | UL | JT |
| Ciaran O'Connell | m | 2007-04-13 | 2007-04-14 | 2 | GST | 800m |
| Cormac O'Connell | m | 1993-02-12 | 1993-11-27 | 2 | UCD | 800m, Road |
| D.F. O'Connell | m | 1961-05-14 | 1962-06-06 | 3 | NACA | 120yH, 4x110y |
| Denis O'Connell | m | 1971-05-07 | 1973-05-16 | 11 | IUAA, UCD | 100m, 200m, 400m, 440y, 4x100m, 4x110y |
| Denis O'Connell | m | 1954-05-22 | 1954-05-22 | 1 | UCC | LJ |
| Douglas O'Connell | m | 2008-11-15 | 2008-11-15 | 1 | UCC | Road |
| Enda O'Connell | m | 1992-01-31 | 1995-03-11 | 19 | IUAA, SPM | 110mH, 60mH, HJ, PV, TJ |
| F. O'Connell | m | 1957-05-18 | 1957-05-18 | 2 | UCC | 120yH, HJ |
| F. O'Connell | m | 1948-05-22 | 1948-05-22 | 1 | UCD | 120yH |
| Fintan O'Connell | m | 2000-11-12 | 2000-11-12 | 1 | UCD | Road |
| Gerry O'Connell | m | 2003-11-22 | 2004-02-28 | 2 | DCU | Road, XC |
| J. O'Connell | m | 1970-03-14 | 1970-03-14 | 1 | TCD | XC |
| Jack O'Connell | m | 2023-04-21 | 2024-04-06 | 12 | GST, TCD | 1500m, 400m, 400mH, 4x200m, 4x400m, CE, HJ, LJ, SP |
| James O'Connell | m | 2022-01-29 | 2024-04-06 | 12 | TCD | 400m, 400mH, LJ, Road |
| Johnathan O'Connell | m | 2003-11-22 | 2004-02-07 | 2 | IT Tralee | 1500m, Road |
| Liam O'Connell | m | 2016-03-05 | 2017-04-08 | 4 | UCC | 5000m, Road, XC |
| Louis O'Connell | m | 2023-01-28 | 2023-04-22 | 4 | UL | 100m, 4x200m, 60m |
| P. O'Connell | m | 1990-04-27 | 1990-04-28 | 1 | UCD | HT |
| P. O'Connell | m | 1977-05-06 | 1977-05-07 | 1 | UCG | 100m |
| Patrick O'Connell | m | 1913-05-24 | 1913-05-24 | 2 | UCD | 56lbWfD, SP |
| Peter O'Connell | m | 2008-11-15 | 2008-11-15 | 1 | UCD | Road |
| Sean O'Connell | m | 1990-03-03 | 1990-03-03 | 1 | UCG | XC |
| W. O'Connell | m | 1967-05-05 | 1968-05-11 | 3 | UCC | HJ, LJ |
| William O'Connell | m | 2002-12-06 | 2002-12-07 | 3 | IT Tralee | 200m, 4x200m, 60mH |
| Brendan O'Conner | m | 2007-12-08 | 2009-04-25 | 11 | WIT | 100m, 200m, 35lbWfD, 4x100m, 4x200m, 60m, LJ, SP |
| ?. O'Connor | m | 1970-05-09 | 1970-05-09 | 1 | SPM | 400m |
| ?. O'Connor | m | 1974-05-03 | 1974-05-04 | 1 | NCPE | HT |
| A. O'Connor | m | 1975-05-02 | 1975-05-03 | 1 | NCPE | HT |
| A. O'Connor | m | 1983-05-06 | 1983-05-07 | 1 | UCD | PV |
| Alan O'Connor | m | 2006-12-02 | 2011-02-05 | 14 | IT Tralee | 35lbWfD, 4x200m, DT, SP |
| Art O'Connor | m | 2013-02-01 | 2014-04-12 | 7 | UCD | 400m, 4x400m |
| Ben O'Connor | m | 2023-11-10 | 2024-04-06 | 3 | UCC | 5000m, Road |
| C. O'Connor | m | 1982-04-30 | 1983-05-07 | 2 | TCE | 400m |
| C. O'Connor | m | 1956-05-16 | 1956-05-16 | 1 | UCC | DT |
| C. O'Connor | m | 1977-03-12 | 1977-03-12 | 1 | UCC | XC |
| Cathal O'Connor | m | 2012-02-04 | 2012-02-04 | 4 | UCC | 60mH, CE, HJ, LJ |
| Conleth O'Connor | m | 1933-07-10 | 1933-07-10 | 1 | The Rest | HJ |
| D. O'Connor | m | 1937-05-22 | 1937-05-22 | 1 | UCD | LJ |
| Danny O'Connor | m | 2013-02-01 | 2014-04-12 | 16 | CIT | 110mH, 4x100m, 60mH, CE, HJ, LJ, SP |
| Darren O'Connor | m | 2014-11-15 | 2014-11-15 | 1 | CIT | Road |
| David "Dave" O'Connor | m | 1973-03-10 | 1975-05-21 | 13 | UCD | 1500m, 5000m, 800m, XC |
| Eamonn O'Connor | m | 2011-03-05 | 2012-02-18 | 4 | TCD | 10000m, XC |
| Eamonn O'Connor | m | 2011-03-12 | 2012-03-10 | 2 | DCU | XC |
| Eoin O'Connor | m | 2019-02-08 | 2019-04-06 | 6 | WIT | 1500m, 3000m, 4x400m, 800m |
| Eoin O'Connor | m | 1998-12-11 | 1999-04-24 | 2 | DIT | DT, SP |
| Eoin O'Connor | m | 1996-04-19 | 1996-12-14 | 2 | UCC | 3000mW, 400m |
| F. O'Connor | m | 1939-05-27 | 1939-05-27 | 3 | UCC | 100y, 220y, LJ |
| Gearoid O'Connor | m | 2000-02-26 | 2003-11-22 | 19 | IT Tallaght, IUAA | 1500m, 3000m, 800m, Road, XC |
| Gerard O'Connor | m | 2001-12-07 | 2001-12-08 | 2 | UU | 200m, 60m |
| J. O'Connor | m | 1972-05-05 | 1972-05-06 | 1 | UCC | TJ |
| Joe O'Connor | m | 2000-12-01 | 2003-03-09 | 9 | IT Tralee | 1500m, 3000m, 3000mSC, 800m, Road, XC |
| Joe O'Connor | m | 1998-12-11 | 1999-12-04 | 6 | IT Tralee | 1500m, 3000m, 3000mSC |
| John O'Connor | m | 1988-04-29 | 1996-04-20 | 9 | GST, ILSI, UCD | DT, HT, SP |
| John O'Connor | m | 1993-02-12 | 1995-06-17 | 10 | Dublin, ILSI, IUAA | 35lbWfD, DT, HT, SP |
| John O'Connor | m | 1971-02-20 | 1974-05-04 | 7 | UCG | 10000m, 1500m, XC |
| K. O'Connor | m | 1989-05-05 | 1989-05-06 | 2 | UCD | LJ, TJ |
| K. O'Connor | m | 1976-04-30 | 1976-05-01 | 1 | NCPE | HT |
| Killian O'Connor | m | 2011-11-12 | 2015-04-11 | 7 | DCU | 3000m, 3000mSC, Road, XC |
| Killian O'Connor | m | 2015-11-14 | 2015-11-14 | 1 | UL | Road |
| Killian O'Connor | m | 2017-03-04 | 2017-03-04 | 1 | UL | XC |
| L. O'Connor | m | 1988-04-29 | 1988-04-30 | 2 | NIHED | HJ, LJ |
| Lorcan O'Connor | m | 2011-04-29 | 2011-04-30 | 6 | UL | 110mH, CE, HJ, LJ, SP |
| M. O'Connor | m | 1970-05-09 | 1970-05-09 | 1 | UCC | HJ |
| M. O'Connor | m | 1989-03-04 | 1989-03-04 | 1 | Cork RTC | XC |
| Martin G. O'Connor | m | 1985-03-09 | 1986-03-08 | 4 | TCD | 3000mSC, 5000m, XC |
| Michael O'Connor | m | 1999-03-06 | 2000-06-20 | 12 | CIT, IUAA | 400m, 4x100m, 4x400m, 800m, Road, XC |
| Michael O'Connor | m | 2003-04-25 | 2004-04-17 | 4 | CIT | 200m, 4x200m, 4x400m |
| Michael O'Connor | m | 2000-12-01 | 2002-04-20 | 7 | CIT | 400m, 4x400m, 60m, 800m |
| N. O'Connor | m | 1981-03-07 | 1981-03-07 | 1 | SPM | XC |
| N. O'Connor | m | 1989-03-04 | 1989-03-04 | 1 | NIHED | XC |
| Neil O'Connor | m | 2001-04-07 | 2001-04-07 | 1 | DIT | XC |
| P. O'Connor | m | 1978-03-04 | 1980-03-01 | 3 | SPM | XC |
| Pat O'Connor | m | 1988-04-29 | 1988-04-30 | 1 | UCD | HT |
| Patrick O'Connor | m | 2013-02-01 | 2016-04-16 | 9 | TCD | 200m, 4x100m, 4x200m, 4x400m, 60m |
| Paul O'Connor | m | 1994-01-21 | 1994-02-19 | 3 | UCG | 200m, 60m, XC |
| Peter O'Connor | m | 2009-11-14 | 2010-11-13 | 4 | UCD | 400m, Road |
| Peter O'Connor | m | 2018-02-09 | 2019-04-06 | 16 | IT Carlow | 60mH, CE, HJ, LJ, SP |
| Rodger O'Connor | m | 1999-11-13 | 1999-11-13 | 1 | CIT | Road |
| Ross O'Connor | m | 2015-04-10 | 2015-04-11 | 1 | CIT | JT |
| Seamus O'Connor | m | 2017-03-04 | 2017-03-04 | 1 | TGC | XC |
| Seamus O'Connor | m | 2002-12-06 | 2004-02-07 | 6 | IT Tralee | 200m, 4x200m, 60m |
| Sean O'Connor | m | 1958-05-18 | 1959-05-17 | 2 | NACA | 440y |
| Sean O'Connor | m | 1968-11-30 | 1969-07-12 | 4 | IUAA, UCD | 3 Miles, Mile, XC |
| Shane O'Connor | m | 2001-11-07 | 2002-11-16 | 3 | TCD | Road |
| Stephen O'Connor | m | 1995-06-17 | 1995-06-20 | 2 | H & Y | HT |
| Stephen O'Connor | m | 1999-12-03 | 1999-12-04 | 2 | DIT | 4x200m, TJ |
| T. O'Connor | m | 1946-07-14 | 1946-07-14 | 1 | UCG | DT |
| T.P. O'Connor | m | 1931-05-30 | 1931-05-30 | 1 | UCC | LJ |
| T' O'Connor | m | 1980-03-01 | 1980-03-01 | 1 | SPM | XC |
| Terry O'Connor | m | 1962-06-06 | 1963-05-19 | 2 | NACA | Mile |
| Tim Pat O'Connor | m | 1996-02-09 | 1997-06-24 | 8 | GST, IUAA, Waterford RTC, WIT | 4x200m, LJ |
| Timothy "Tim" O'Connor | m | 1946-07-14 | 1946-07-14 | 1 | UCD | 4x440y |
| Timothy Patrick "Tim" O'Connor | m | 1969-05-03 | 1973-05-16 | 27 | TCD | DT, JTo, SP |
| Tom O'Connor | m | 1991-03-02 | 1993-03-06 | 4 | DCU | 5000m, XC |
| W. O'Connor | m | 1959-05-17 | 1959-05-17 | 1 | NACA | 100y |
| William O'Connor | m | 2014-04-11 | 2016-04-16 | 5 | UL | 400m, 4x100m, 4x400m |
| Abmurf O'Cuinn | m | 2014-03-08 | 2014-04-12 | 2 | CIT | PV, XC |
| Gerard O'Daly | m | 1997-12-12 | 1998-04-25 | 7 | WIT | 110mH, 400mH, 60mH, LJ, TJ, XC |
| Daren O'Dea | m | 1995-12-16 | 1995-12-16 | 1 | UU | XC |
| Darren O'Dea | m | 1994-01-21 | 1997-12-13 | 10 | UU | 400m, 400mH, 4x200m, 800m |
| Francis J. O'Dea | m | 1920-06-05 | 1922-06-10 | 9 | UCD | 100y, 220y, 440y, 880y |
| Kevin O'Dea | m | 2004-02-06 | 2004-02-07 | 1 | GST | SP |
| C. O'Doherty | m | 1932-05-28 | 1932-05-28 | 1 | UCD | 100y |
| C.J. O'Doherty | m | 1933-05-27 | 1934-05-26 | 10 | IUAA, UCD | 100y, 120yH, 220y, 880y, 220yx2, 440y |
| Eamonn O'Doherty | m | 1925-06-06 | 1929-07-03 | 8 | IUAA, UCD | DT, SP |
| Ger O'Doherty | m | 1982-03-06 | 1982-03-06 | 1 | UCD | XC |
| Gerry O'Doherty | m | 1988-03-05 | 1989-05-06 | 4 | UU | 5000m, XC |
| Brian O'Donaghue | m | 1998-01-31 | 2004-02-28 | 12 | GST, IUAA, President's Select, UCD | 800m, Road, XC |
| Brendan O'Donnell | m | 2020-02-15 | 2023-04-22 | 10 | DCU | 35lbWfD, HJ, HT, SP |
| Brendan O'Donnell | m | 2009-11-14 | 2011-03-12 | 5 | TCD | 1500m, 800m, Road, XC |
| Brian O'Donnell | m | 1996-02-09 | 1998-12-12 | 6 | UU | 2000mW, 3000mW |
| Cathal O'Donnell | m | 2023-11-10 | 2023-11-10 | 1 | UCD | Road |
| Cian O'Donnell | m | 2018-05-26 | 2018-05-26 | 2 | Scotland | 200m, 4x100m |
| Dara O'Donnell | m | 2021-11-13 | 2021-11-13 | 1 | TCD | Road |
| E. O'Donnell | m | 1965-05-19 | 1966-05-18 | 7 | IUAA, UCD | 440y, 880y |
| Eamon O'Donnell | m | 2001-04-20 | 2002-04-20 | 2 | WIT | 400mH, 4x400m |
| Eamonn O'Donnell | m | 2001-12-07 | 2002-04-20 | 5 | WIT | 400mH, 4x200m, 800m |
| Eoghan O'Donnell | m | 1998-02-28 | 1998-02-28 | 1 | WIT | XC |
| Eoin O'Donnell | m | 1998-04-24 | 1998-04-25 | 1 | WIT | 3000mSC |
| Eric O'Donnell | m | 1989-03-04 | 1992-04-25 | 6 | UCD | 3000mSC, 5000m, XC |
| Eric O'Donnell | m | 1993-02-12 | 1995-06-17 | 4 | ILSI, IUAA | 10000m, 3000m, 5000m |
| F. O'Donnell | m | 1983-05-06 | 1983-05-07 | 1 | UCD | 3000mW |
| Gary O'Donnell | m | 2002-03-09 | 2002-03-09 | 1 | UU | XC |
| Gerald P. O'Donnell | m | 1913-05-24 | 1913-05-24 | 2 | UCD | 880y, Mile |
| Gerard O'Donnell | m | 2011-02-05 | 2014-04-12 | 19 | AIT | 200m, 400m, 400mH, 4x100m, 4x200m, 60mH |
| Gerard O'Donnell | m | 2007-12-08 | 2008-04-19 | 7 | UL | 400m, 400mH, 4x100m, 4x200m, 4x400m |
| Gerard O'Donnell | m | 2016-04-15 | 2016-04-16 | 1 | GST | 110mH |
| J. O'Donnell | m | 1977-03-12 | 1977-03-12 | 1 | UCG | XC |
| Jamie O'Donnell | m | 1988-04-29 | 1993-04-24 | 7 | GST, ILSI, UCD | 35lbWfD, JT, SP |
| Joe O'Donnell | m | 2009-02-14 | 2009-04-25 | 3 | UG | 800m |
| Joe O'Donnell | m | 1975-03-08 | 1977-05-07 | 3 | UCG | 1500m, XC |
| Kevin O'Donnell | m | 1997-04-25 | 1997-04-26 | 1 | Limerick RTC | 3000mSC |
| Killian O'Donnell | m | 2014-11-15 | 2014-11-15 | 1 | DCU | Road |
| Liam O'Donnell | m | 2000-11-12 | 2011-04-30 | 37 | QUB | 200m, 400m, 400mH, 4x100m, 4x200m, 4x400m, Road |
| M. O'Donnell | m | 1978-03-04 | 1978-03-04 | 1 | NUU | XC |
| Mark O'Donnell | m | 2006-12-02 | 2009-04-25 | 7 | WIT | 200m, 4x100m, 4x200m |
| Martin O'Donnell | m | 1998-04-24 | 1998-04-25 | 3 | UU | 100m, 200m |
| Niall O'Donnell | m | 1994-06-28 | 1999-06-22 | 3 | GST, IUAA, NI U20 | 100m, 200m |
| P. O'Donnell | m | 1977-03-12 | 1977-03-12 | 1 | NUU | XC |
| Patrick O'Donnell | m | 2014-05-31 | 2014-05-31 | 1 | SUCA | PV |
| Patrick O'Donnell | m | 2022-04-08 | 2022-04-09 | 1 | UCD | 4x100m |
| Patrick O'Donnell | m | 2005-12-10 | 2006-04-22 | 6 | UU | 400mH, 4x200m, 4x400m, 60mH, 800m |
| Paul O'Donnell | m | 2018-03-10 | 2020-03-07 | 7 | UCD | 3000mSC, Road, XC |
| Richard O'Donnell | m | 2000-11-12 | 2003-03-09 | 5 | TCD, UG | Road, XC |
| Seamus O'Donnell | m | 2000-12-01 | 2000-12-02 | 1 | GST | 2000mW |
| Seamus O'Donnell | m | 1980-03-01 | 1985-03-09 | 5 | UCG | XC |
| Stephen O'Donnell | m | 2013-11-23 | 2014-02-07 | 4 | UG | 1500m, 3000m, Road |
| Stephen O'Donnell | m | 2014-11-15 | 2015-03-07 | 2 | DCU | Road, XC |
| Stephen O'Donnell | m | 2017-03-04 | 2017-03-04 | 1 | MU | XC |
| Stephen O'Donnell | m | 2018-02-09 | 2019-11-16 | 6 | MU | 3000m, 5000m, Road, XC |
| Thomas Francis O'Donnell | m | 1927-06-04 | 1927-06-28 | 4 | IUAA, TCD | 220y, 440y, 220yx2, 880y |
| Turlough O'Donnell | m | 2001-11-07 | 2001-11-07 | 1 | GST | Road |
| Brian O'Donoghue | m | 1997-12-12 | 2000-04-15 | 7 | UCD | 1500m, 2000mW, 800m |
| Brian O'Donoghue | m | 2003-04-25 | 2004-02-07 | 5 | UCD | 1500m, 4x400m |
| Brian O'Donoghue | m | 1996-02-09 | 2001-04-21 | 12 | UCC | 100m, 200m, 400m, 4x100m, LJ |
| Brian O'Donoghue | m | 2010-11-13 | 2010-11-13 | 1 | UCD | Road |
| C. O'Donoghue | m | 1975-03-08 | 1975-03-08 | 1 | UCC | XC |
| Ciaran O'Donoghue | m | 2012-07-18 | 2012-07-18 | 1 | IUAA | 400m |
| Conor O'Donoghue | m | 2009-11-14 | 2009-11-14 | 1 | UCC | Road |
| Daniel O'Donoghue | m | 2005-04-22 | 2005-04-23 | 2 | RCSI | 10000m, 1500m |
| James O'Donoghue | m | 1995-12-16 | 1996-04-20 | 4 | UL | 5000m, 800m, XC |
| James O'Donoghue | m | 1996-12-13 | 1996-12-14 | 1 | UCC | 1500m |
| John O'Donoghue | m | 2007-11-17 | 2007-11-17 | 1 | UCC | Road |
| Jonathan O'Donoghue | m | 2017-02-18 | 2017-03-04 | 2 | UCD | XC |
| Kevin O'Donoghue | m | 1995-12-16 | 1996-02-10 | 3 | UL | 1500m, XC |
| Maurice O'Donoghue | m | 2006-12-02 | 2007-04-14 | 5 | UL | 400m |
| N. O'Donoghue | m | 1946-07-14 | 1946-07-14 | 3 | UCD | 100y, 220y, 4x440y |
| Niall O'Donoghue | m | 2004-11-20 | 2004-11-20 | 1 | UL | Road |
| P. O'Donoghue | m | 1985-05-03 | 1985-05-04 | 1 | UU | 10000m |
| Peter O'Donoghue | m | 1989-03-04 | 1993-03-06 | 5 | UU | 10000m, XC |
| Ronan O'Donoghue | m | 2007-11-17 | 2011-03-12 | 7 | CIT | 3000mSC, Road, XC |
| Thomas O'Donoghue | m | 1998-06-23 | 1998-06-23 | 5 | IUAA | 110mH, 4x100m, HT, PV, SP |
| Thomas O'Donoghue | m | 1998-04-24 | 1999-04-24 | 11 | GST, UG | 110mH, CE, DT, HJ, JT, LJ, SP |
| Tom O'Donoghue | m | 1996-12-13 | 1997-12-13 | 9 | UCG, UG | 200m, 4x200m, LJ, SP, TJ, XC |
| Tom O'Donoghue | m | 2000-04-14 | 2001-06-19 | 8 | AIT, IUAA | 100m, HJ, HT, JT, LJ, PV |
| Barry O'Donohoe | m | 2009-02-14 | 2010-04-07 | 8 | UCD | 100m, 4x100m, 4x200m, 60m |
| Barry O'Donovan | m | 2008-11-15 | 2012-04-21 | 17 | UCC | 10000m, 12, 4, 8, 16, 3000m, DT, Road, XC |
| Cathal O'Donovan | m | 2010-03-13 | 2014-02-22 | 4 | TCD | XC |
| Cillian O'Donovan | m | 2015-11-14 | 2018-11-17 | 7 | UCC | 1500m, 4x400m, 5000m, Road, XC |
| Conor O'Donovan | m | 2019-03-02 | 2023-03-04 | 6 | UCC | Road, XC |
| D. O'Donovan | m | 1967-05-05 | 1968-05-11 | 4 | UCC | 100y, 120yH, 220y, PV |
| D.C. O'Donovan | m | 1927-06-04 | 1927-06-04 | 1 | UCD | HJ |
| Daniel O'Donovan | m | 2008-04-18 | 2008-04-19 | 2 | UCC | 4x400m, 800m |
| Darren O'Donovan | m | 2002-12-06 | 2008-04-19 | 35 | UCC | 100m, 200m, 4x100m, 4x200m, 4x400m, 60m |
| Declan O'Donovan | m | 1992-03-07 | 1994-02-19 | 3 | DCU | XC |
| Fergus O'Donovan | m | 1960-05-14 | 1963-02-16 | 3 | UCC | 880y, XC |
| H. O'Donovan | m | 1975-05-02 | 1975-05-03 | 1 | UCG | HJ |
| Ian O'Donovan | m | 2005-11-19 | 2005-11-19 | 1 | UCC | Road |
| Jack O'Donovan | m | 2021-11-13 | 2023-03-04 | 3 | UCC | Road, XC |
| John O'Donovan | m | 1946-07-14 | 1952-05-22 | 9 | UCC | 100y, 120yH, 220y, 440y, 880y |
| Kevin O'Donovan | m | 1996-04-13 | 1998-02-28 | 4 | UL | 1500m, CE, XC |
| Killian O'Donovan | m | 2012-11-17 | 2012-11-17 | 1 | CIT | Road |
| Mark O'Donovan | m | 2009-03-07 | 2009-03-07 | 1 | CIT | XC |
| Pat O'Donovan | m | 2001-02-24 | 2001-02-24 | 1 | TCD | XC |
| S. O'Donovan | m | 1950-05-17 | 1950-05-17 | 1 | UCD | DT |
| T. O'Donovan | m | 1982-03-06 | 1982-03-06 | 1 | SPM | XC |
| T. Fergus O'Donovan | m | 1961-05-06 | 1963-05-11 | 4 | IUAA, UCC | 880y, Mile |
| Briain O'Dowd | m | 2004-12-03 | 2007-04-14 | 8 | DIT | 3000m, 3000mSC, 4x200m, Road, XC |
| D. O'Dowd | m | 1989-03-04 | 1989-03-04 | 1 | TCE | XC |
| F. O'Dowd | m | 1988-03-05 | 1989-03-04 | 2 | SPM | XC |
| P. O'Dowd | m | 1978-03-04 | 1978-03-04 | 1 | SPM | XC |
| Padraic O'Dowd | m | 1991-03-02 | 1991-03-02 | 1 | SPM | XC |
| T. O'Dowd | m | 1970-05-09 | 1970-05-09 | 2 | UCG | LJ |
| James O'Driscell | m | 2008-11-15 | 2009-04-25 | 2 | CIT | 5000m, Road |
| Barry O'Driscoll | m | 1998-12-11 | 1999-04-24 | 3 | DCU | 800m |
| Darren O'Driscoll | m | 1999-12-03 | 2001-04-21 | 9 | UCC | 100m, 200m, 4x200m, 60m, JT, LJ |
| Dean O'Driscoll | m | 1986-05-02 | 1989-03-04 | 2 | UCC | 5000m, XC |
| Frank O'Driscoll | m | 1968-05-11 | 1970-05-13 | 5 | UCC, UCD | 100y, LJ |
| James O'Driscoll | m | 2009-03-07 | 2013-03-09 | 12 | CIT | 1500m, 400mH, 5000m, Road, XC |
| Jeremy O'Driscoll | m | 2006-12-02 | 2006-12-03 | 3 | CIT | 400m, 4x200m, LJ |
| Padraig O'Driscoll | m | 2012-04-11 | 2014-04-12 | 17 | UCD | 100m, 4x100m, 4x200m, 60m, CE, HJ, JT, LJ, SP |
| Sean O'Driscoll | m | 1986-03-08 | 1988-03-05 | 2 | UCC | XC |
| Sean O'Driscoll | m | 2018-02-09 | 2020-02-15 | 10 | DCU | 100m, 4x100m, 4x200m, 60m |
| Padraig O'Dubhgain | m | 1997-02-01 | 2001-04-07 | 10 | CIT | 1500m, 3000m, Road, XC |
| Paudie O'Duggain | m | 2000-04-14 | 2000-04-15 | 2 | CIT | 800m |
| B. O'Dwyer | m | 1986-03-08 | 1986-03-08 | 1 | UCC | XC |
| C. O'Dwyer | m | 1988-04-29 | 1989-05-06 | 2 | NIHED | 3000mSC, 800m |
| Ciaran O'Dwyer | m | 1978-05-05 | 1980-12-06 | 3 | UCD | 1500m, XC |
| Ciaran O'Dwyer | m | 1982-03-06 | 1982-03-06 | 1 | TCD | XC |
| Darren O'Dwyer | m | 2022-04-08 | 2022-11-11 | 2 | DCU | 800m, Road |
| E. O'Dwyer | m | 1958-05-18 | 1958-07-28 | 2 | IUAA, UCD | DT, TJ |
| J. O'Dwyer | m | 1979-03-17 | 1979-03-17 | 1 | UCC | XC |
| K. O'Dwyer | m | 1988-03-05 | 1988-03-05 | 1 | NIHED | XC |
| Kieran O'Dwyer | m | 1977-03-12 | 1981-05-13 | 6 | UCD | 1500m, XC |
| Kieran O'Dwyer | m | 1982-04-30 | 1982-05-12 | 2 | TCD | 10000m, 5000m |
| Kieran O'Dwyer | m | 1997-02-01 | 1997-02-01 | 1 | UCC | XC |
| Owen O'Dwyer | m | 2006-11-18 | 2007-02-24 | 2 | TCD | Road, XC |
| Ray O'Dwyer | m | 2012-04-20 | 2012-04-21 | 2 | GST | DP, SS |
| Rory O'Dwyer | m | 1964-05-31 | 1964-05-31 | 1 | NACA | TJ |
| Sean O'Dwyer | m | 1962-06-06 | 1966-05-18 | 30 | IUAA, NACA, UCD | 4x110y, HJ, LJ, TJ |
| Shane O'Dwyer | m | 2011-02-05 | 2014-04-12 | 25 | IUAA, WIT | 200m, 4x100m, 4x200m, 4x400m, HJ, LJ, XC |
| Maitiú O'Fáphorta | m | 2006-12-02 | 2006-12-03 | 1 | UL | 60m |
| Feargus O'Farell | m | 2014-11-15 | 2014-11-15 | 1 | UCD | Road |
| F. O'Farrell | m | 1983-03-12 | 1983-03-12 | 1 | NIHEL | XC |
| Jack O'Farrell | m | 2012-02-04 | 2012-02-04 | 3 | UG | 400m, 4x200m |
| Lt. Mick O'Farrell | m | 1958-05-18 | 1960-05-15 | 7 | NACA | 120yH, JTo, TJ |
| Lt. Mick O'Farrell | m | 1963-05-19 | 1963-05-19 | 3 | Army | 4x110y, LJ, TJ |
| Robert O'Farrell | m | 2002-12-06 | 2004-04-17 | 7 | TCD | 35lbWfD, 400m, DT, JT, SP |
| Colman O'Flaherty | m | 1978-06-30 | 1978-06-30 | 1 | President's Select | 100m |
| David O'Flaherty | m | 1977-05-06 | 1977-05-07 | 4 | UCG | 100m, 200m |
| Derry O'Flaherty | m | 1991-03-02 | 1991-03-02 | 1 | UCC | XC |
| Gerry O'Flaherty | m | 1988-03-05 | 1988-03-05 | 1 | UCG | XC |
| Gerry O'Flaherty | m | 1989-03-04 | 1992-03-07 | 3 | UCG | XC |
| J.A. O'Flaherty | m | 1921-06-04 | 1923-06-02 | 7 | UCD | 100y, 220y, 440y |
| Oran O'Flaherty | m | 2018-03-10 | 2018-03-10 | 1 | UCD | XC |
| P. O'Flaherty | m | 1946-07-14 | 1946-07-14 | 1 | UCG | LJ |
| Naoise O'Flaitheartaigh | m | 2019-11-16 | 2023-04-22 | 10 | UL | 3000m, 5000m, Road, XC |
| Kevin P. O'Flanagan | m | 1939-05-27 | 1939-05-27 | 1 | UCD | LJ |
| Cormac O'Floinn | m | 2018-02-09 | 2018-02-09 | 2 | TGC | 1500m |
| Colm O'Flynn | m | 2001-12-07 | 2002-04-20 | 3 | UCC | 200m, TJ |
| John Joe O'Flynn | m | 1969-03-01 | 1972-03-04 | 4 | UCC | 800m, XC |
| Micky O'Flynn | m | 1967-05-05 | 1968-05-11 | 6 | IUAA, UCC | 220y, LJ, TJ |
| Micky O'Flynn | m | 1978-06-30 | 1978-06-30 | 1 | IUAA | TJ |
| Paul O'Flynn | m | 2004-02-06 | 2004-02-07 | 1 | CIT | LJ |
| Conal Ó'gadhra | m | 2017-11-18 | 2018-02-09 | 3 | UCC | 1500m, Road |
| Oisin O'Gibne | m | 2017-11-18 | 2022-04-09 | 14 | AIT | 1500m, 4x200m, 4x400m, 800m, Road, XC |
| Ruarcan O'Gibne | m | 2019-11-16 | 2019-11-16 | 1 | DCU | Road |
| Donal O'Gorman | m | 1991-03-02 | 1994-04-23 | 5 | TCE, UL | 3000mSC, 3000mW, CE, XC |
| G. O'Gorman | m | 1961-05-06 | 1964-05-31 | 4 | IUAA, UCG | 440y |
| P. O'Gorman | m | 1971-02-20 | 1973-03-10 | 3 | SPM | XC |
| Paddy O'Gorman | m | 1999-12-03 | 2005-04-23 | 36 | CIT, IUAA | 100m, 200m, 400m, 4x100m, 4x200m, 4x400m, 60m, XC |
| Roderic O'Gorman | m | 2000-11-12 | 2001-11-07 | 4 | TCD | Road, XC |
| Simon O'Gorman | m | 1985-05-03 | 1985-05-04 | 1 | NIHED | 100m |
| Stephen O'Gorman | m | 2004-02-06 | 2006-04-22 | 13 | DIT | 100m, 200m, 4x100m, 4x400m, 60m |
| T. O'Gorman | m | 1982-03-06 | 1982-03-06 | 1 | UCC | XC |
| Pat O'Grady | m | 1991-03-02 | 1991-03-02 | 1 | UL | XC |
| Brian O'Hagan | m | 2015-02-06 | 2016-04-16 | 7 | IT Carlow | 1500m, 3000m, 4x400m, 5000m, Road |
| Darragh O'Hagan | m | 2001-04-07 | 2001-04-07 | 1 | TCD | XC |
| Deaglan O'Hagan | m | 2001-12-07 | 2003-11-22 | 6 | UU | 1500m, 200m, 60m, LJ, Road, XC |
| Anthony "Tony" O'Halloran | m | 1991-03-02 | 1993-04-24 | 7 | DCU | 10000m, 5000m, XC |
| Ashley O'Halloran | m | 2000-04-14 | 2001-04-21 | 7 | CIT | 110mH, 400mH, HJ, JT |
| Brian O'Halloran | m | 1957-05-18 | 1961-06-01 | 12 | IUAA, UCD | DT, JTo, SP |
| Damien O'Halloran | m | 2003-11-22 | 2004-11-20 | 2 | NUIM | Road |
| David O'Halloran | m | 2013-02-01 | 2013-02-01 | 4 | UCD | 200m, 4x200m, 60m |
| Edmund O'Halloran | m | 2011-02-05 | 2014-05-31 | 45 | IUAA, UCC | 100m, 110mH, 200m, 4x100m, 4x200m, 4x400m, 60m, 60mH, Road |
| Joseph O'Halloran | m | 2002-11-16 | 2003-04-26 | 4 | CIT | 2000mW, 3000mW, Road, XC |
| Morgan O'Halloran | m | 2004-11-20 | 2004-11-20 | 1 | TCD | Road |
| T. O'Halloran | m | 1982-03-06 | 1982-03-06 | 1 | UCC | XC |
| B. O'Hanlon | m | 1971-02-20 | 1971-02-20 | 1 | UCC | XC |
| Cdt. W. O'Hanlon | m | 1963-05-19 | 1963-05-19 | 1 | Army | 440y |
| Domhnaill O'Hanlon | m | 2006-11-18 | 2007-11-17 | 2 | UCD | Road |
| Michael F. O'Hanlon | m | 1912-06-03 | 1913-05-24 | 2 | UCD | LJ |
| P. O'Hanlon | m | 1977-05-06 | 1977-05-07 | 1 | TCD | LJ |
| Richard O'Hannrachain | m | 2011-11-12 | 2012-03-10 | 2 | TCD | Road, XC |
| Risteard O'Hannrachain | m | 2015-04-10 | 2015-04-11 | 1 | UCD | 10000m |
| Ferdia O'Haodha | m | 2008-03-08 | 2010-03-13 | 6 | DCU | 3000mSC, 3000mW, Road, XC |
| Chris O'Hara | m | 2002-11-16 | 2002-11-16 | 1 | GST | Road |
| Killian O'Hara | m | 2013-11-23 | 2015-04-11 | 7 | ITB | 4x200m, 800m, Road |
| Andy O'Hare | m | 2003-04-25 | 2004-02-07 | 7 | UU | 100m, 110mH, CE, HJ, LJ, SP |
| Fearghal O'Hare | m | 2021-11-13 | 2022-01-29 | 3 | TCD | 800m, Road |
| James O'Hare | m | 2010-04-23 | 2013-04-13 | 10 | QUB | 1500m, 5000m, Road, XC |
| Neill O'Hare | m | 1985-05-03 | 1988-04-30 | 2 | NIHED | DT |
| P. O'Hare | m | 1989-03-04 | 1989-03-04 | 1 | SPM | XC |
| Tony O'Hare | m | 2004-12-03 | 2004-12-04 | 1 | UG | TJ |
| Sean O'Héigeartaigh | m | 2002-12-06 | 2008-03-28 | 18 | IUAA, TCD | 10000m, 3000m, 3000mSC, 5000m, Road, XC |
| Tom O'Herlihy | m | 1994-04-22 | 1994-04-23 | 1 | UCC | DT |
| Dara O'Hogain | m | 2000-11-12 | 2001-02-24 | 2 | TCD | Road, XC |
| L. O'Hora | m | 1982-03-06 | 1982-03-06 | 1 | TCE | XC |
| Promice O'Kafor | m | 2016-02-12 | 2016-04-16 | 6 | CIT | 4x100m, 4x200m, LJ, TJ |
| H. O'Kane | m | 1971-02-20 | 1971-02-20 | 1 | SPM | XC |
| M. O'Kane | m | 1983-03-12 | 1983-03-12 | 1 | NUU | XC |
| Sam O'Kane | m | 2013-06-01 | 2016-05-28 | 12 | SU, SUCA | DT, HT, SP |
| Conor O'Keefe | m | 2015-03-07 | 2015-03-07 | 1 | UCD | XC |
| Conor O'Keefe | m | 2019-11-16 | 2021-11-13 | 2 | TCD | Road |
| Stephen O'Keefe | m | 2008-11-15 | 2008-11-15 | 1 | UCC | Road |
| Tom O'Keefe | m | 2015-11-14 | 2018-11-17 | 13 | Ireland, IUAA, UCD | 3000m, 5000m, 800m, Road, XC |
| Andrew O'Keeffe | m | 2013-11-23 | 2014-11-15 | 2 | CIT | Road |
| Colman O'Keeffe | m | 1972-03-04 | 1975-05-03 | 5 | UCC | 400m, TJ, XC |
| Conor O'Keeffe | m | 2017-11-18 | 2019-03-02 | 3 | UCD | Road, XC |
| David O'Keeffe | m | 2015-11-14 | 2017-11-18 | 6 | UCD | 3000mSC, Road, XC |
| Diarmuid O'Keeffe | m | 2011-11-12 | 2011-11-12 | 1 | UCD | Road |
| Eamon O'Keeffe | m | 1967-05-27 | 1968-05-11 | 5 | BLE, UCD | 440y, 880y |
| Eoghan O'Keeffe | m | 1994-02-19 | 1998-05-02 | 25 | IUAA, UL | 400m, 400mH, 4x200m, CE, HT, JT, PV, XC |
| Luke O'Keeffe | m | 2012-04-20 | 2012-04-21 | 2 | UCC | 4x400m |
| M. O'Keeffe | m | 1983-03-12 | 1983-05-07 | 2 | NIHEL | 3000mW, XC |
| Michael B. "Mick" O'Keeffe | m | 1973-05-11 | 1976-05-11 | 10 | TCD | DT, HT, SP |
| Pat O'Keeffe | m | 1993-03-06 | 1997-04-26 | 16 | GST, IUAA, UCC | 1500m, 3000m, 800m, Road, XC |
| Sean O'Keeffe | m | 1992-03-07 | 1992-03-07 | 1 | Cork RTC | XC |
| Sgt. Joe O'Keeffe | m | 1962-06-06 | 1963-05-19 | 2 | Army | 3 Miles |
| T. O'Keeffe | m | 1979-03-17 | 1980-03-01 | 2 | UCG | XC |
| Cpl. S. O'Kelly | m | 1961-05-14 | 1961-05-14 | 1 | Army | PV |
| Fionan O'Kelly | m | 1959-05-17 | 1959-05-17 | 1 | NACA | 880y |
| Pte P. O'Kelly | m | 1961-05-14 | 1961-05-14 | 1 | Army | 880y |
| Stephen O'Kennedy | m | 2015-11-14 | 2017-03-04 | 6 | TCD | 1500m, Road, XC |
| Aidan O'Leary | m | 2012-04-20 | 2012-04-21 | 1 | CIT | LJ |
| Alan O'Leary | m | 2001-12-07 | 2002-12-07 | 10 | UG | 100m, 200m, 400m, 4x100m, 4x400m, 60m, HJ |
| Alan O'Leary | m | 1996-12-13 | 1998-12-12 | 3 | UL | 400m, 800m |
| Andrew O'Leary | m | 2001-04-20 | 2001-04-21 | 2 | IT Tallaght | 100m, 200m |
| Aonghus O'Leary | m | 1979-03-17 | 1979-03-17 | 1 | UCG | XC |
| Bobby O'Leary | m | 1995-06-17 | 1995-06-17 | 1 | Dublin | 3000mW |
| Colum O'Leary | m | 2013-03-09 | 2017-03-04 | 21 | IUAA, TCD | 1500m, 3000m, 3000mSC, 5000m, Road, XC |
| D. O'Leary | m | 1973-03-10 | 1976-03-06 | 3 | UCC | XC |
| F. O'Leary | m | 1977-03-12 | 1977-03-12 | 1 | UCC | XC |
| Greg O'Leary | m | 2005-12-10 | 2009-04-25 | 14 | DCU | 200m, 400m, 400mH, 4x200m, 4x400m |
| Ian O'Leary | m | 1994-04-22 | 1994-06-28 | 2 | GST, UCC | 5000m |
| Ian "Jumbo" O'Leary | m | 1989-03-04 | 1994-02-19 | 11 | UCC | 10000m, 3000m, 5000m, Road, XC |
| Jack O'Leary | m | 1962-05-17 | 1966-11-19 | 6 | UCC | Mile, XC |
| John O'Leary | m | 2010-03-13 | 2010-03-13 | 1 | IT Tallaght | XC |
| Karl O'Leary | m | 1994-02-19 | 1994-02-19 | 1 | Cork RTC | XC |
| L. O'Leary | m | 1959-05-17 | 1961-05-14 | 2 | NACA | HJ |
| Michael O'Leary | m | 2002-12-06 | 2004-04-17 | 6 | IT Carlow | 100m, 200m, 60m |
| P. O'Leary | m | 1976-03-06 | 1976-03-06 | 1 | SPM | XC |
| Sean O'Leary | m | 2019-03-02 | 2022-04-09 | 4 | DCU | 10000m, 5000m, Road, XC |
| Shay O'Leary | m | 2014-02-22 | 2014-02-22 | 1 | UCD | XC |
| Ted O'Leary | m | 2016-11-19 | 2016-11-19 | 1 | UCC | Road |
| Tony O'Leary | m | 1973-03-10 | 1976-03-06 | 6 | UCC | 1500m, 5000m, 800m, XC |
| Seamus O'Loan | m | 1991-03-02 | 1992-04-25 | 4 | TCD | 10000m, XC |
| Sean O'Loingsigh | m | 2002-12-06 | 2002-12-07 | 3 | UCD | 200m, 60m |
| Mairtin O'Loinsigh | m | 2007-12-08 | 2007-12-09 | 2 | GMIT | 35lbWfD, SP |
| Sean O'Loinsigh | m | 2004-02-06 | 2004-04-17 | 5 | UCD | 200m, 400m, 4x100m, 4x200m |
| Cian O'Loughlin | m | 2009-02-14 | 2010-02-13 | 5 | TCD | 4x200m, 60m, LJ |
| Ross O'Loughlin | m | 2006-12-02 | 2010-04-24 | 25 | WIT | 1500m, 200m, 400m, 4x100m, 4x200m, 4x400m, 800m, JT, Road, XC |
| Rian O'Luasa | m | 2023-11-10 | 2023-11-10 | 1 | UCD | Road |
| D. O'Mahoney | m | 1970-03-14 | 1970-03-14 | 1 | UCC | XC |
| E. O'Mahoney | m | 1922-06-10 | 1922-06-10 | 1 | UCD | 120yH |
| M.C. O'Mahoney | m | 1922-06-10 | 1922-06-10 | 2 | UCC | 880y, Mile |
| T. O'Mahoney | m | 1952-05-22 | 1952-05-22 | 1 | UCD | 100y |
| Alan O'Mahony | m | 1999-04-23 | 1999-04-24 | 3 | WIT | 100m, 4x400m |
| C O'Mahony | m | 1955-05-19 | 1955-05-19 | 1 | UCC | Mile |
| Conor O'Mahony | m | 2015-11-14 | 2019-04-06 | 10 | UL | 10000m, 3000m, Road, XC |
| D. O'Mahony | m | 1976-03-06 | 1976-03-06 | 1 | UCC | XC |
| Daniel Edward "Donal" O'Mahony | m | 1979-03-17 | 1982-05-12 | 9 | TCD | 1500m, 3000mSC, DT, XC |
| David O'Mahony | m | 2004-12-03 | 2004-12-04 | 1 | CIT | 60m |
| Declan O'Mahony | m | 1995-04-21 | 1996-04-20 | 3 | Cork RTC | 100m, LJ |
| Declan O'Mahony | m | 1996-02-09 | 1996-02-10 | 1 | GST | 400m |
| Donnacha O'Mahony | m | 1985-03-09 | 1992-03-07 | 15 | UCC | 10000m, 1500m, 3000mSC, 5000m, Road, XC |
| Francis O'Mahony | m | 1999-12-03 | 2006-12-03 | 30 | IUAA, WIT | 4x200m, 4x400m, 800m, Road |
| John O'Mahony | m | 1939-05-27 | 1939-05-27 | 2 | UCC | 100y, 220y |
| K. O'Mahony | m | 1969-03-01 | 1969-03-01 | 1 | UCC | XC |
| M.C. O'Mahony | m | 1921-06-04 | 1921-06-04 | 2 | UCC | 440y, 880y |
| S. O'Mahony | m | 1985-05-03 | 1985-05-04 | 1 | UCC | 200m |
| T. O'Mahony | m | 1983-05-06 | 1983-05-07 | 1 | UCG | JTo |
| T. O'Mahony | m | 1967-05-05 | 1968-05-11 | 2 | UCC | 120yH |
| Brendan O'Malley | m | 1986-03-08 | 1988-04-30 | 3 | UCG | 1500m, XC |
| C. O'Malley | m | 1976-04-30 | 1976-05-01 | 1 | NCPE | PV |
| Damien O'Malley | m | 1999-04-23 | 1999-04-24 | 1 | IT Carlow | 4x100m |
| Johnathan O'Malley | m | 2006-02-18 | 2006-02-18 | 1 | UCD | XC |
| P. O'Malley | m | 1962-05-17 | 1962-05-17 | 1 | UCG | JTo |
| P. O'Malley | m | 1968-05-11 | 1968-05-11 | 1 | UCG | TJ |
| Sean O'Maoilmhichil | m | 2002-11-16 | 2004-02-07 | 5 | IT Tralee | 400m, Road, XC |
| Declan O'Meara | m | 2023-11-10 | 2024-03-09 | 4 | TUD | 3000m, Road, XC |
| Diarmuid O'Meara | m | 2000-12-01 | 2004-04-17 | 54 | IUAA, UCC | 100m, 110mH, 200m, 35lbWfD, 400mH, 4x100m, 4x200m, 60mH, CE, DT, HJ, HT, LJ, PV, SP, TJ |
| Duirmuid O'Meara | m | 2001-04-20 | 2001-04-20 | 1 | UCC | CE |
| J.P. O'Meara | m | 1936-05-30 | 1936-05-30 | 2 | UCD | 880y, Mile |
| Michael "Mike" O'Meara | m | 1973-03-10 | 1975-03-08 | 2 | UCG | XC |
| Michael "Mike" O'Meara | m | 1979-03-17 | 1979-03-17 | 1 | UCG | XC |
| P. O'Meara | m | 1970-05-09 | 1970-05-09 | 1 | UCC | SP |
| P.B. O'Meara | m | 1937-05-22 | 1939-05-27 | 3 | UCD | Mile |
| M. O'Moran | m | 1988-04-29 | 1988-04-30 | 1 | SPM | HT |
| Joeseph O'Muiracheartaigh | m | 2003-11-22 | 2004-02-28 | 2 | DIT | Road, XC |
| Jerome John O'Mullane | m | 1913-05-24 | 1914-06-06 | 6 | UCC | 120yH, 440y, LJ |
| Paul O'Neil | m | 2012-07-18 | 2014-03-08 | 4 | Lagan Valley AC, QUB | 400m, XC |
| Warren O'Neil | m | 2007-11-17 | 2007-11-17 | 1 | TCD | Road |
| ?. O'Neill | m | 1988-03-05 | 1988-03-05 | 1 | TCE | XC |
| A. O'Neill | m | 1934-05-26 | 1934-05-26 | 1 | UCC | 100y |
| B. O'Neill | m | 1966-05-07 | 1966-05-07 | 2 | TCD | 440y, 880y |
| Breandan O'Neill | m | 2007-11-17 | 2011-03-12 | 10 | DCU | 3000m, 5000m, Road, XC |
| Brendan O'Neill | m | 1971-02-20 | 1976-05-01 | 10 | UCG | 1500m, 3000mSC, XC |
| Brian O'Neill | m | 2020-02-15 | 2020-02-15 | 3 | AIT | 4x200m, 60m |
| Brian O'Neill | m | 1971-02-20 | 1975-03-08 | 4 | UCC | 3000mSC, XC |
| Brian Clarke O'Neill | m | 1964-11-21 | 1968-05-11 | 10 | TCD | 440y, 880y, Mile, XC |
| Colin O'Neill | m | 1990-04-27 | 1993-03-06 | 4 | UU | 10000m, 3000mSC, XC |
| Colm O'Neill | m | 1992-03-07 | 1992-03-07 | 1 | UU | XC |
| Donal O'Neill | m | 1991-05-03 | 1994-04-23 | 2 | QUB | HJ, LJ |
| Eamon O'Neill | m | 2010-03-13 | 2011-03-12 | 2 | IT Tallaght | XC |
| Eoghan O'Neill | m | 1999-12-03 | 1999-12-04 | 1 | IT Tallaght | 200m |
| Eoin O'Neill | m | 1994-02-19 | 1994-04-23 | 2 | QUB | 1500m, XC |
| Eoin O'Neill | m | 1993-06-22 | 1993-06-22 | 1 | IUAA | 800m |
| Eoin O'Neill | m | 1997-06-24 | 1998-06-23 | 2 | GST | Mile |
| Eugene O'Neill | m | 1995-12-16 | 2005-04-23 | 31 | DIT, GST, IUAA, TCD | 1500m, 3000m, 3000mSC, 4x400m, 5000m, Mile, Road, XC |
| Gerard O'Neill | m | 2013-04-12 | 2014-02-07 | 2 | UU | 800m, SP |
| I. O'Neill | m | 1986-03-08 | 1986-03-08 | 1 | UU | XC |
| Ian O'Neill | m | 1988-03-05 | 2002-11-16 | 11 | GST, IUAA, NI U23, UU | 10000m, 5000m, Road, XC |
| J. O'Neill | m | 1958-07-28 | 1958-07-28 | 1 | UCD | 440y |
| Jack O'Neill | m | 1952-05-22 | 1953-07-15 | 4 | UCD | 100y, 220y |
| James O'Neill | m | 2018-04-13 | 2020-02-15 | 7 | DCU, Ireland | 35lbWfD, DT, SP |
| Jimmy K. O'Neill | m | 1956-05-16 | 1958-05-18 | 5 | IUAA, UCD | 440y, 880y |
| Michael O'Neill | m | 2009-11-14 | 2009-11-14 | 1 | CIT | Road |
| Patrick O'Neill | m | 2022-01-29 | 2024-04-06 | 18 | QUB | 110mH, 200m, 400m, 400mH, 4x200m, 4x400m, 60mH |
| Robert O'Neill | m | 2013-04-12 | 2013-04-13 | 1 | UCC | 3000mW |
| S. O'Neill | m | 1985-05-03 | 1985-05-04 | 1 | UCC | 800m |
| Sean O'Neill | m | 1973-03-10 | 1973-03-10 | 1 | UCC | XC |
| Shane O'Neill | m | 1995-12-16 | 1998-03-14 | 6 | Dublin Colleges, TCD | 1500m, Road, XC |
| Shelby O'Neill | m | 2013-11-23 | 2013-11-23 | 1 | TCD | Road |
| Tony O'Neill | m | 1997-12-12 | 1999-03-06 | 3 | DCU | 3000m, XC |
| Angel Albert O'Perez | m | 2000-04-14 | 2000-04-15 | 1 | IT Tralee | LJ |
| S. O'Raghailleagh | m | 1981-03-07 | 1981-03-07 | 1 | UCD | XC |
| Shane O'Rahilly | m | 2012-11-17 | 2017-04-08 | 30 | WIT | 1500m, 400m, 4x400m, 5000m, 800m, Road, XC |
| Alan O'Reagan | m | 2001-04-07 | 2001-04-21 | 2 | UG | JT, XC |
| Brendan O'Regan | m | 1969-05-03 | 1972-05-06 | 11 | UCC | 100m, 100y, 200m, 220y, 4x100m |
| Brendan O'Regan | m | 1974-05-03 | 1974-05-04 | 1 | UCG | 100m |
| Cyril O'Regan | m | 1967-05-27 | 1967-05-27 | 2 | BLE | 4x110y, LJ |
| Jake O'Regan | m | 2011-11-12 | 2016-04-16 | 9 | UL | 10000m, 5000m, Road, XC |
| Michael O'Regan | m | 2008-11-15 | 2011-04-30 | 19 | CIT | 1500m, 400m, 400mH, 4x100m, 4x400m, 800m, LJ, Road, XC |
| Michael Pat O'Regan | m | 2011-11-12 | 2012-04-21 | 6 | CIT | 4x400m, 5000m, 800m, Road, XC |
| A. O'Reilly | m | 1991-03-02 | 1991-03-02 | 1 | DCU | XC |
| Aichlinn O'Reilly | m | 2015-03-07 | 2015-03-07 | 1 | UL | XC |
| Alan O'Reilly | m | 1996-12-13 | 1996-12-14 | 7 | WIT | 200m, 400m, 4x200m |
| Alan O'Reilly | m | 2008-11-15 | 2013-04-13 | 11 | CIT | 10000m, 3000mW, Road, SP, XC |
| Aodhagan O'Reilly | m | 2008-11-15 | 2014-03-08 | 10 | UCD | 3000m, 5000m, Road, XC |
| Brendan O'Reilly | m | 1964-05-30 | 1964-05-30 | 1 | AAUE | HJ |
| Brendan O'Reilly | m | 1960-05-14 | 1960-05-14 | 2 | UCD | HJ, JTo |
| Cathal O'Reilly | m | 2021-11-13 | 2024-04-06 | 10 | DCU | 10000m, 1500m, 3000mSC, Road, XC |
| Cian O'Reilly | m | 2011-04-29 | 2016-02-12 | 16 | IUAA, UCD | 1500m, 3000m, 5000m, Road, XC |
| D. O'Reilly | m | 1988-03-05 | 1988-03-05 | 1 | NIHED | XC |
| D. O'Reilly | m | 1991-03-02 | 1991-03-02 | 1 | Cork RTC | XC |
| Eugene O'Reilly | m | 2003-04-25 | 2003-04-26 | 1 | UG | 800m |
| Fionan O'Reilly | m | 2006-11-18 | 2010-11-13 | 14 | UCD | 1500m, 3000mSC, LJ, Road, XC |
| Franklin O'Reilly | m | 2010-11-13 | 2010-11-13 | 1 | DCU | Road |
| J.F. O'Reilly | m | 1935-05-25 | 1935-05-25 | 2 | UCD | 880y, Mile |
| John O'Reilly | m | 1983-05-06 | 1986-03-08 | 3 | TCE | 10000m, XC |
| John O'Reilly | m | 1993-12-04 | 1997-04-26 | 10 | UCD | 1500m, 800m, XC |
| K. O'Reilly | m | 1960-05-14 | 1960-05-15 | 2 | IUAA, UCD | 440y |
| K. O'Reilly | m | 1986-03-08 | 1986-03-08 | 1 | NIHED | XC |
| Lawrence O'Reilly | m | 2011-04-29 | 2015-04-11 | 28 | AIT | 100m, 200m, 4x100m, 4x200m, 60m, LJ |
| M. O'Reilly | m | 1958-05-18 | 1958-05-18 | 1 | NACA | 880y |
| Martin O'Reilly | m | 1999-12-03 | 1999-12-04 | 2 | DIT | 60m |
| Matthew O'Reilly | m | 2007-12-08 | 2012-04-21 | 11 | IT Carlow | 35lbWfD, DT, SP |
| Michael O'Reilly | m | 2006-11-18 | 2006-11-18 | 1 | TCD | Road |
| Niall O'Reilly | m | 2010-11-13 | 2010-11-13 | 1 | NUIM | Road |
| P. O'Reilly | m | 1964-02-15 | 1964-02-15 | 1 | UCD | XC |
| P. O'Reilly | m | 1969-05-03 | 1969-05-03 | 1 | RCSI | 3 Miles |
| Patrick Joseph "Paddy" O'Reilly | m | 1977-05-17 | 1980-05-14 | 12 | TCD | DT, SP |
| S. O'Reilly | m | 1980-03-01 | 1980-03-01 | 1 | UCD | XC |
| Senan O'Reilly | m | 1980-05-02 | 1992-04-25 | 12 | UCD | 10000m, 1500m, 3000mSC, 5000m, XC |
| Shane O'Reilly | m | 2013-02-01 | 2013-02-01 | 4 | UCD | CE, HJ, LJ, SP |
| Stephen O'Reilly | m | 1996-02-09 | 1996-11-23 | 4 | TCD | 400m, 4x200m, Road, XC |
| T. O'Reilly | m | 1963-11-16 | 1964-02-15 | 2 | UCD | XC |
| Trevor O'Reilly | m | 1996-02-09 | 1996-02-10 | 2 | GST | 60m, LJ |
| Mattew O'Reily | m | 2009-02-14 | 2009-04-25 | 4 | IT Carlow | 35lbWfD, DT, SP |
| Benen O'Riain | m | 2019-11-16 | 2023-03-04 | 6 | QUB | Road, XC |
| Brendan O'Riain | m | 2012-04-11 | 2012-04-11 | 2 | UCD | 100m, 200m |
| C.P. O'Riordan | m | 1936-05-30 | 1936-05-30 | 2 | UCG | 880y, Mile |
| Cian O'Riordan | m | 2019-11-16 | 2023-03-04 | 3 | UL | Road, XC |
| Colm O'Riordan | m | 1938-05-26 | 1939-05-27 | 3 | UCG | 880y, Mile |
| Darragh O'Riordan | m | 2012-11-17 | 2012-11-17 | 1 | NUIM | Road |
| Don O'Riordan | m | 2002-12-06 | 2002-12-07 | 2 | CIT | 200m, 60m |
| Donal O'Riordan | m | 1990-03-03 | 1992-04-25 | 3 | UCD | 1500m, XC |
| Eamonn O'Riordan | m | 1974-05-03 | 1976-05-01 | 3 | NCPE | PV |
| Graham O'Riordan | m | 2008-11-15 | 2008-11-15 | 1 | UCC | Road |
| Martin O'Riordan | m | 2005-11-19 | 2005-11-19 | 1 | CIT | Road |
| Michael O'Riordan | m | 1975-03-08 | 1980-05-03 | 4 | UCC | 110mH, 400mH, XC |
| Pat O'Riordan | m | 1977-06-14 | 1977-06-14 | 1 | BLE Select | 3000mSC |
| Patrick "Pat" O'Riordan | m | 1964-02-15 | 1969-07-12 | 14 | IUAA, UCC | 3 Miles, 880y, Mile, XC |
| Stephen O'Riordan | m | 2011-02-05 | 2011-04-30 | 6 | DIT | CE, HJ, LJ, SP, TJ |
| Tom O'Riordan | m | 1964-05-30 | 1964-05-30 | 1 | AAUE | Mile |
| Aaron O'Rourke | m | 2001-11-07 | 2001-11-07 | 1 | UCD | Road |
| C. O'Rourke | m | 1982-04-30 | 1982-05-01 | 1 | UCC | 3000mSC |
| Conor O'Rourke | m | 2012-02-04 | 2012-04-21 | 2 | UG | 4x400m, 800m |
| Conor O'Rourke | m | 2013-03-09 | 2016-04-16 | 19 | UCD | 3000mW, 60mH, CE, HJ, JT, LJ, SP, XC |
| Cormac O'Rourke | m | 2019-11-16 | 2019-11-16 | 1 | QUB | Road |
| Declan O'Rourke | m | 1998-12-11 | 1998-12-12 | 4 | TCD | 400m, 4x200m |
| Fraser O'Rourke | m | 2014-05-31 | 2019-05-25 | 3 | SAL Select, Scotland, SUCA | PV |
| Killian O'Rourke | m | 1996-12-13 | 1996-12-14 | 4 | QUB | 200m, 4x200m, 60m, LJ |
| Neil O'Rourke | m | 2007-02-24 | 2008-11-15 | 3 | UU | Road, XC |
| Neil O'Rourke | m | 2015-03-07 | 2015-03-07 | 1 | UCD | XC |
| Robert O'Rourke | m | 2002-04-19 | 2004-04-17 | 11 | IT Carlow | 1500m, 4x400m, 800m, XC |
| Stephen O'Rourke | m | 2010-02-13 | 2010-02-13 | 2 | WIT | 35lbWfD, SP |
| William "Billy" O'Rourke | m | 1981-03-07 | 1985-05-04 | 5 | UCC | 10000m, 3000mSC, XC |
| T.R. O'Scanaill | m | 1967-05-05 | 1967-05-05 | 1 | UCC | SP |
| Diarmuid Ó'Séaghdha | m | 2000-02-05 | 2004-02-28 | 13 | TCD | 10000m, 5000m, Road, XC |
| Cathal O'Seanain | m | 2012-11-17 | 2014-04-12 | 3 | UG | 10000m, Road, XC |
| Shane O'Shaughnessey | m | 2000-11-12 | 2000-11-12 | 1 | CIT | Road |
| G. O'Shaughnessy | m | 1988-04-29 | 1990-03-03 | 2 | UCC | 1500m, XC |
| Tom O'Shaughnessy | m | 1976-04-30 | 1982-05-12 | 29 | UCD, UCG | DT, HT, JT, JTo, SP |
| Alan O'Shea | m | 1999-11-13 | 2006-04-22 | 20 | UCC | 10000m, 1500m, 5000m, 800m, Road, XC |
| Alan O'Shea | m | 2013-04-12 | 2013-04-13 | 1 | TCD | 10000m |
| B. O'Shea | m | 1976-03-06 | 1976-03-06 | 1 | SPM | XC |
| B. O'Shea | m | 1989-03-04 | 1989-03-04 | 1 | UCC | XC |
| Brendan O'Shea | m | 1965-03-06 | 1966-02-19 | 3 | UCG | XC |
| Brendan O'Shea | m | 1978-03-04 | 1978-03-04 | 1 | UCG | XC |
| Brendan O'Shea | m | 1995-02-10 | 1998-02-28 | 20 | GST, IUAA, UCD | 400m, 800m, HJ, LJ, TJ, XC |
| David O'Shea | m | 2007-12-08 | 2012-04-21 | 35 | DCU, UL | 100m, 200m, 4x100m, 4x200m, 4x400m, 60m |
| Diarmuid O'Shea | m | 2023-11-10 | 2024-03-09 | 3 | TCD | 800m, Road, XC |
| Eugene O'Shea | m | 1978-05-05 | 1981-03-07 | 4 | UCG | 1500m, XC |
| Fintan O'Shea | m | 1977-05-06 | 1980-05-03 | 4 | UCC | LJ, TJ |
| Fionn O'Shea | m | 2012-03-10 | 2012-03-10 | 1 | DCU | XC |
| Ger O'Shea | m | 2002-12-06 | 2004-04-17 | 7 | UL | 1500m, 3000mW, 400m, 4x400m, 800m, JT, Road |
| Gerard O'Shea | m | 2005-12-10 | 2012-04-21 | 29 | GST, UL | 200m, 400m, 4x100m, 4x200m, 4x400m, 60m |
| J. O'Shea | m | 1989-05-05 | 1989-05-06 | 2 | NIHEL | JT, SP |
| James O'Shea | m | 2021-11-13 | 2022-11-11 | 3 | UCC | Road, XC |
| M O'Shea | m | 1962-05-17 | 1962-05-17 | 1 | UCG | 4x110y |
| Michael O'Shea | m | 2017-04-07 | 2017-04-08 | 2 | UL | 400m, 4x100m |
| Michael O'Shea | m | 2001-12-07 | 2004-04-17 | 8 | UL | 200m, 3000mW, 4x400m, 800m, Road |
| Michael "Mick" O'Shea | m | 1971-02-20 | 1972-03-04 | 2 | SPM | XC |
| Pat O'Shea | m | 1960-05-14 | 1961-05-14 | 3 | IUAA, NACA, UCC | HJ |
| Peter O'Shea | m | 2018-04-13 | 2019-05-25 | 3 | Ireland, TCD | JT |
| Peter O'Shea | m | 2019-02-08 | 2022-04-09 | 3 | DCU | 60mH, JT |
| S. O'Shea | m | 1991-05-03 | 1991-05-04 | 1 | UL | JT |
| Sgt F. O'Shea | m | 1964-05-31 | 1967-05-27 | 5 | Army | DT, JT |
| Sgt. F. O'Shea | m | 1961-05-14 | 1961-05-14 | 3 | Army | DT, JTo, SP |
| T. O'Shea | m | 1959-05-13 | 1959-05-13 | 1 | UCC | HJ |
| Daithí Ó'Shionaigh | m | 2017-04-07 | 2017-04-08 | 2 | UCC | 1500m |
| Aidan O'Sullivan | m | 1998-04-24 | 1998-04-25 | 1 | UL | JT |
| Brendan O'Sullivan | m | 1991-03-02 | 1991-03-02 | 1 | UCC | XC |
| C. O'Sullivan | m | 1986-03-08 | 1986-03-08 | 1 | UCC | XC |
| Carl O'Sullivan | m | 2009-03-07 | 2012-02-18 | 11 | TCD | 1500m, 3000m, 5000m, Road, XC |
| Conall "Connie" O'Sullivan | m | 1961-05-06 | 1961-05-06 | 2 | UCC | 220y, LJ |
| Cpl M. O'Sullivan | m | 1965-06-22 | 1965-06-22 | 1 | Army | LJ |
| D. O'Sullivan | m | 1959-05-17 | 1959-05-17 | 1 | NACA | PV |
| D. O'Sullivan | m | 1979-05-04 | 1983-05-07 | 6 | TCE, UCD | JT, JTo, PV |
| D. O'Sullivan | m | 1934-05-26 | 1936-05-30 | 3 | UCG | DT, SP |
| Daniel O'Sullivan | m | 1991-03-02 | 1991-03-02 | 1 | DIT | XC |
| Daniel Joseph O'Sullivan | m | 1914-06-06 | 1914-06-06 | 2 | UCC | DT, HJ |
| David O'Sullivan | m | 1998-02-28 | 1999-11-13 | 2 | CIT | Road, XC |
| Denis O'Sullivan | m | 2004-04-16 | 2007-04-14 | 7 | WIT | 1500m, 5000m, 800m, XC |
| Domhnall O'Sullivan | m | 2006-11-18 | 2006-11-18 | 1 | TCD | Road |
| Donal O'Sullivan | m | 1970-03-14 | 1970-03-14 | 1 | UCC | XC |
| Donal O'Sullivan | m | 2013-11-23 | 2013-11-23 | 1 | UCC | Road |
| Eamonn N.M. O'Sullivan | m | 1922-06-10 | 1923-06-02 | 2 | UCD | DT, JTo |
| Eoin O'Sullivan | m | 2000-02-26 | 2000-04-15 | 2 | CIT | 1500m, XC |
| Eoin O'Sullivan | m | 2007-11-17 | 2008-03-08 | 2 | CIT | Road, XC |
| Eoin O'Sullivan | m | 2022-04-08 | 2022-04-09 | 4 | UCD | 4x100m, 4x400m |
| G. O'Sullivan | m | 1986-03-08 | 1986-03-08 | 1 | UCG | XC |
| Garry O'Sullivan | m | 2016-11-19 | 2017-04-08 | 4 | UCC | 800m, Road |
| Gary O'Sullivan | m | 1995-12-16 | 1995-12-16 | 1 | UCC | XC |
| Gary O'Sullivan | m | 1998-04-24 | 1998-04-25 | 1 | DIT | PV |
| Gavin O'Sullivan | m | 2005-02-26 | 2009-03-07 | 10 | UL | 1500m, Road, XC |
| Gavin O'Sullivan | m | 2010-03-13 | 2010-03-13 | 1 | CIT | XC |
| Harry O'Sullivan | m | 2015-03-07 | 2015-03-07 | 1 | IT Tralee | XC |
| Ian O'Sullivan | m | 1994-01-21 | 2008-03-08 | 70 | Cork RTC, DCU, IUAA, Queen's Select, UCC | 10000m, 110mH, 1500m, 2000mSC, 3000m, 3000mSC, 400mH, 4x400m, 5000m, 800m, Road, TJ, XC |
| J. O'Sullivan | m | 1980-03-01 | 1980-03-01 | 1 | UCC | XC |
| J.F. O'Sullivan | m | 1934-05-26 | 1934-05-26 | 1 | UCC | 220y |
| Jack O'Sullivan | m | 2012-11-17 | 2013-11-23 | 2 | DCU | Road |
| James O'Sullivan | m | 1985-05-03 | 1985-05-04 | 1 | TCE | JTo |
| Jerome Ivo O'Sullivan | m | 1912-06-03 | 1912-06-03 | 1 | UCC | 440y |
| John O'Sullivan | m | 2017-04-07 | 2019-02-08 | 14 | UCC | 100m, 200m, 4x100m, 4x200m |
| John O'Sullivan | m | 1996-02-09 | 1996-02-10 | 5 | GST | 200m, 60m, LJ, TJ |
| John Joe O'Sullivan | m | 1929-06-01 | 1934-05-26 | 13 | UCC | 100y, 220y, 440y, 880y |
| Liam O'Sullivan | m | 2009-03-07 | 2009-03-07 | 1 | UCC | XC |
| M.J. O'Sullivan | m | 1932-05-28 | 1937-05-22 | 20 | UCD | 100y, 220y, 440y |
| Marcus O'Sullivan | m | 2024-04-05 | 2024-04-06 | 2 | RCSI | 5000m |
| Mark O'Sullivan | m | 2012-11-17 | 2016-04-16 | 18 | CIT | 10000m, 1500m, 3000m, 3000mSC, 5000m, Road, XC |
| Mark O'Sullivan | m | 2003-11-22 | 2003-11-22 | 1 | UCC | Road |
| Martin O'Sullivan | m | 1994-04-22 | 1996-12-14 | 8 | IUAA, UCC | HT, JT, SP |
| Martin O'Sullivan | m | 2011-11-12 | 2014-04-12 | 22 | CIT | 110mH, 35lbWfD, CE, HJ, LJ, Road, SP, XC |
| Martin Moss O'Sullivan | m | 1997-04-25 | 1997-04-26 | 1 | UCC | DT |
| Michael O'Sullivan | m | 2011-02-05 | 2011-02-05 | 2 | IT Tralee | 800m |
| Michael O'Sullivan | m | 2015-02-21 | 2015-02-21 | 1 | TCD | XC |
| Michael O'Sullivan | m | 2017-02-10 | 2019-05-25 | 11 | Ireland, UCD | DT, SP |
| Michael O'Sullivan | m | 1995-04-21 | 1995-04-22 | 1 | UCC | HT |
| Michael O'Sullivan | m | 2005-12-10 | 2007-04-14 | 17 | DCU | 200m, 400m, 4x100m, 4x200m, 4x400m |
| Micheal O'Sullivan | m | 2004-11-20 | 2005-04-23 | 5 | DCU | 400m, 4x100m, 4x400m, Road |
| P.J. O'Sullivan | m | 1952-05-22 | 1961-05-14 | 7 | NACA, UCG | 880y, Mile |
| Paul O'Sullivan | m | 1998-03-14 | 1998-03-14 | 1 | Welsh Universities | XC |
| Peter O'Sullivan | m | 2001-12-07 | 2002-04-20 | 4 | DCU | 100m, 200m, 4x100m, 4x200m |
| Pte Sean O'Sullivan | m | 1964-05-31 | 1966-03-28 | 3 | Army | 3 Miles |
| Richard O'Sullivan | m | 2011-04-29 | 2011-04-30 | 3 | UCC | 800m, LJ, SP |
| Richie O'Sullivan | m | 2006-11-18 | 2008-04-19 | 4 | UCC | 200m, 400m, 60m, Road |
| Sean O'Sullivan | m | 2002-12-06 | 2004-04-17 | 24 | CIT | 110mH, 400m, 4x200m, 4x400m, 60mH, CE, HJ, LJ, PV, SP |
| Sean O'Sullivan | m | 2014-11-15 | 2016-04-16 | 8 | UL | 1500m, 3000mSC, 5000m, Road, XC |
| Sean O'Sullivan | m | 2017-04-07 | 2017-04-08 | 1 | UL | 1500m |
| Stephen O'Sullivan | m | 2002-11-16 | 2002-11-16 | 1 | CIT | Road |
| T.J. O'Sullivan | m | 1921-06-04 | 1921-06-04 | 1 | UCD | SP |
| Tomas O'Sullivan | m | 2009-04-24 | 2013-02-01 | 18 | UCC | 200m, 400m, 4x100m, 4x200m, 4x400m |
| Vincent O'Sullivan | m | 2000-12-01 | 2005-02-05 | 18 | GST, President's Select, UCD | 1500m, 2000mW, 3000m, 3000mW, 5000m, Road, XC |
| W.M. O'Sullivan | m | 1930-06-07 | 1930-06-07 | 1 | UCC | 440y |
| Josh O'Sullivan Hourihan | m | 2011-11-12 | 2016-04-16 | 17 | IUAA, UCC | 1500m, 3000m, 3000mSC, Road, XC |
| Zac O'Sullivan Hourihan | m | 2017-11-18 | 2017-11-18 | 1 | UCC | Road |
| Donal O'Sullivian | m | 2004-11-20 | 2004-11-20 | 1 | UCC | Road |
| Conall O'Toole | m | 2019-02-08 | 2020-02-15 | 8 | TCD | 200m, 4x100m, 4x200m, 4x400m |
| Conall O'Toole | m | 2023-01-28 | 2024-04-06 | 5 | TCD | 200m, 400m, 4x400m, Mixed 4x400m |
| John O'Toole | m | 1998-02-28 | 1998-02-28 | 1 | UCD | XC |
| John O'Toole | m | 1977-03-12 | 1978-05-17 | 5 | UCD | 10000m, 5000m, XC |
| Ross O'Toole | m | 2018-11-17 | 2019-11-16 | 3 | UCD | Road, XC |
| S. O'Toole | m | 1976-12-04 | 1976-12-04 | 1 | UCD | XC |
| B. O'Tuama | m | 1972-05-05 | 1972-05-06 | 1 | UCC | 10000m |
| Cillian O'Tuama | m | 1997-02-01 | 2005-04-23 | 10 | IUAA, UCC | 10000m, Road, XC |
| E. O'Tuama | m | 1977-03-12 | 1977-03-12 | 1 | UCC | XC |
| Killan O'Tuama | m | 1999-11-13 | 2004-04-17 | 4 | UCC | 10000m, Road, XC |
| Billy Oakes | m | 1979-05-04 | 1986-05-03 | 21 | UCC | 100m, LJ, TJ |
| Peter Obidiran | m | 2022-01-29 | 2022-01-29 | 3 | IT Carlow | 200m, 4x200m |
| Patrick Obijuru | m | 2017-02-10 | 2017-02-10 | 1 | ITB | 60m |
| Patrick Obogone | m | 2005-04-22 | 2005-04-23 | 2 | DCU | LJ, SP |
| Eanna Obradaigh | m | 2022-01-29 | 2022-04-09 | 4 | TCD | 1500m, XC |
| Abraham Odekeye | m | 2023-01-28 | 2023-04-22 | 3 | DCU | 35lbWfD, HJ |
| Elijah Odigie | m | 2024-04-05 | 2024-04-06 | 1 | DKIT | 4x100m |
| Philip Edwin Odlum | m | 1973-05-11 | 1975-05-21 | 6 | TCD | DT, PV, SP |
| Stephen L. Odlum | m | 1974-05-03 | 1974-05-15 | 5 | TCD | DT, HT, JTo, SP |
| Kaodichinma Ogbene | m | 2013-02-01 | 2016-04-16 | 36 | CIT | 100m, 200m, 4x100m, 4x200m, 4x400m, 60m |
| Ucne Ogbene | m | 2015-02-06 | 2015-02-06 | 3 | UCC | 4x200m, 60m |
| Emmanual Ogbonna | m | 2014-02-07 | 2019-04-06 | 14 | Ireland, IUAA, WIT | LJ, TJ |
| David Oghuvbu | m | 2023-11-28 | 2023-11-28 | 1 | DCU | 60m |
| Ore Ogunde | m | 2012-04-20 | 2012-04-21 | 4 | IT Carlow | 100m, 4x100m, PV |
| Kenny Ogundipe | m | 2023-04-21 | 2024-02-10 | 4 | UCD | 200m, 4x200m, 4x400m |
| Malik Ogungbo | m | 2014-02-07 | 2015-02-06 | 5 | IT Carlow | 200m, 400m, 4x200m |
| John Ogunjemilusi | m | 2019-02-08 | 2019-04-06 | 4 | UCC | 100m, 4x100m, 60m |
| Michael Ogunsiakan | m | 2020-02-15 | 2022-04-09 | 5 | TUD | 4x100m, 4x200m, 60m |
| Jubril Folawamiri Ojewale | m | 2023-01-28 | 2023-04-22 | 3 | MU | 100m, 4x100m, 60m |
| Joseph Ojewumi | m | 2015-02-06 | 2019-02-08 | 23 | DCU | 100m, 200m, 4x100m, 60m |
| Charles Okafor | m | 2022-01-29 | 2023-04-22 | 13 | DCU | 100m, 200m, 4x100m, 4x200m, 4x400m, 60m |
| Steve Okakpu | m | 2010-04-23 | 2010-04-24 | 2 | ITB | 4x100m |
| Elvis Okoh | m | 2023-01-28 | 2024-04-06 | 6 | UCD | LJ, TJ |
| Osazemen Hamsley Okomah | m | 2024-02-10 | 2024-04-06 | 9 | ATU | 100m, 200m, 4x100m, 4x200m, 60m |
| Dennis Okoro | m | 1961-05-06 | 1963-05-22 | 5 | IUAA, UCD | HJ |
| Ugo Kamsi Okpegbuo | m | 2024-04-05 | 2024-04-06 | 2 | ATU | 35lbWfD, SP |
| Abiodum Olabiyi | m | 2004-02-06 | 2004-04-17 | 3 | LIT | 200m, 3000m, XC |
| Samuel Oladunjoye | m | 2014-02-07 | 2014-02-07 | 1 | AIT | SP |
| Praise Olatoke | m | 2018-05-26 | 2018-05-26 | 2 | Scotland | 100m, 4x400m |
| Israel Olatunde | m | 2020-02-15 | 2020-02-15 | 2 | UCD | 60m |
| Israel Olatunde | m | 2022-01-29 | 2023-04-22 | 7 | UCD | 100m, 4x100m, 60m |
| Bruno Oliveira | m | 2010-03-13 | 2010-03-13 | 1 | IT Tallaght | XC |
| P. Oliver | m | 1976-04-30 | 1976-05-01 | 1 | UCC | HT |
| Paul Olla | m | 2019-02-08 | 2019-11-16 | 4 | MU | 1500m, Road |
| Paul Olla | m | 2022-04-08 | 2022-04-09 | 1 | MU | 1500m |
| Samuel Olo | m | 2014-02-07 | 2014-04-12 | 9 | TCD | 100m, 200m, 4x100m, 4x200m, 4x400m |
| Michael Olsen | m | 2018-05-26 | 2018-05-26 | 1 | GST | 100m |
| A. Olsson | m | 1995-03-11 | 1995-03-11 | 1 | SU | SP |
| Olanrewaju O.A. "Afolabi" Olumide | m | 1979-05-23 | 1979-05-23 | 1 | TCD | TJ |
| Rolus Olusa | m | 2016-02-12 | 2017-04-08 | 15 | GST, MU | 110mH, 4x100m, CE, DT, HJ, JT, LJ, SP |
| Rolus Olusa | m | 2018-02-09 | 2019-02-08 | 4 | MU | 60mH |
| Ronan Olwill | m | 2002-03-09 | 2002-03-09 | 1 | DIT | XC |
| Chris Omisore | m | 2017-02-10 | 2017-04-08 | 3 | AIT | 4x100m, TJ |
| Philip Omisore | m | 2022-01-29 | 2022-04-09 | 5 | TUD | 4x200m, 4x400m, 60mH |
| Eseosa Omoregbe | m | 2022-01-29 | 2024-04-06 | 7 | DKIT | 400m, 4x100m, 800m |
| Eseosa Omoregbe | m | 2022-11-11 | 2023-04-22 | 4 | DKIT | 1500m, 800m, Road |
| Michael Ondrej | m | 2008-11-15 | 2010-04-07 | 2 | TCD | 3000m, Road |
| Simon Ong | m | 2009-04-24 | 2009-04-25 | 1 | DIT | 100m |
| Chibuikem Onwumer | m | 2024-04-05 | 2024-04-06 | 4 | TUD | 100m, 200m, 4x100m |
| Nkemjika Onwumereh | m | 2023-04-21 | 2024-04-06 | 11 | DCU | 100m, 4x100m, 4x200m, 60m |
| Jaco Oosthuysen | m | 2013-04-12 | 2015-05-31 | 6 | DIT, IUAA | JT |
| Matthew Opperman | m | 2015-02-06 | 2015-04-11 | 5 | IADT | 100m, 200m, 4x200m |
| Paul Oppermann | m | 2009-02-14 | 2009-04-25 | 5 | UCD | 400m, 4x200m, 4x400m |
| Philip Andrew Orr | m | 1973-05-11 | 1973-05-16 | 2 | TCD | SP |
| Emanuel Osas | m | 2024-02-10 | 2024-04-06 | 13 | DCU | 110mH, 4x100m, 60mH, CE, HJ, LJ, SP |
| Emmanuel Osas | m | 2023-11-28 | 2023-11-28 | 1 | DCU | 60m |
| Ryan Osborne | m | 2012-07-18 | 2012-07-18 | 1 | Dromore AC | 100m |
| B. Oscar | m | 1976-03-06 | 1977-03-12 | 2 | SPM | XC |
| Peter Oshagbemi | m | 1997-06-24 | 1999-06-22 | 2 | NI U23 | 100m, LJ |
| Babafemi Oseleye Osoba | m | 1961-06-01 | 1962-05-23 | 4 | TCD | LJ, PV, TJ |
| Ryan Oswald | m | 2014-05-31 | 2014-05-31 | 2 | SAL Select | 200m, 4x100m |
| A.N. Other | m | 1874-05-16 | 2023-11-28 | 2785 | AAUE, AIT, Army, Atalanta, Birmingham, BLE Select, CIT, Combined Universities, Cork RTC, Cornell-Pennsylvania, DCU, DIT, Dublin, Edinburgh, English Unis, GST, H & Y, IT Carlow, IT Tallaght, IUAA, Loughborough, NACA, NCPE, NI U20, NI U23, NIAAA Select, NIHED, NIHEL, NUIM, NUU, President's Select, QUB, RCSI, SPM, SU, SUCA, TCD, TCE, Tralee RTC, UCC, UCD, UCG, UG, UL, Unknown, UU, WIT | 100m, 100y, 110mH, 120yH, 1500m, 200m, 220y, 3 Miles, 400m, 400mH, 440y, 440yH, 4x100m, 4x100y, 4x110y, 4x200m, 4x400m, 4x440y, 5000m, 800m, 880y, 880y, 220yx2, 440y, 880y, 440y, 220yx2, DT, HJ, HT, JT, JTo, LJ, Mile, PV, Road, SP, TJ, XC |
| Alex Otte | m | 1993-12-04 | 1993-12-04 | 1 | TCD | XC |
| Benjamin Aima Ovbiagele | m | 1961-06-01 | 1965-06-22 | 8 | IUAA, TCD | DT, SP |
| B. Owen | m | 1980-05-14 | 1980-05-14 | 1 | UCD | PV |
| Denis Owen | m | 1992-03-07 | 1992-03-07 | 1 | QUB | XC |
| Cathal Owens | m | 2010-02-13 | 2013-06-01 | 27 | CIT, IUAA | 400m, 400mH, 4x100m, 4x200m, 4x400m |
| Declan Owens | m | 2016-02-12 | 2016-02-12 | 1 | UG | 60m |
| Declan Owens | m | 2018-04-13 | 2018-04-14 | 1 | UG | 4x100m |
| J. Owens | m | 1994-06-28 | 1994-06-28 | 1 | NI U20 | SP |
| John Owens | m | 1965-05-08 | 1965-05-19 | 2 | TCD | PV, SP |
| Ken Owens | m | 1988-02-01 | 1988-02-01 | 1 | Cork RTC | Road |
| Richard Owens | m | 2009-11-14 | 2015-04-11 | 38 | IUAA, UCD | 1500m, 4x200m, 4x400m, 5000m, 800m, Mile, Road, XC |
| Rory Owens | m | 2015-11-14 | 2017-11-18 | 8 | TCD | 3000m, 5000m, Road, XC |
| Sean Owens | m | 2022-11-11 | 2024-03-09 | 5 | TCD | 800m, Road, XC |
| Sheriff Oyebalmji | m | 2009-04-24 | 2009-04-25 | 2 | IT Tallaght | 100m, SP |
| Basit Oyebanji | m | 2022-01-29 | 2024-02-10 | 8 | UCC | 100m, 4x200m, 60m |
| Steven Oyinlola | m | 2022-04-08 | 2023-04-22 | 4 | MU | 100m, 4x100m |
| Patrick "Pat" O.C. Ozieh | m | 1954-05-22 | 1955-05-19 | 7 | UCC | 100y, 120yH, HJ, JTo, LJ |
| Lia O Brien | f | 2022-01-29 | 2022-04-09 | 6 | CIT | 4x100m, 4x200m, DT, LJ |
| Lia O Brien | f | 2023-01-28 | 2024-04-06 | 12 | GST, MTU | 20lbWfD, 4x100m, DT, LJ, TJ |
| Roisin O Brien | f | 2024-03-09 | 2024-03-09 | 1 | UG | XC |
| Denise O Connor | f | 2017-02-10 | 2020-02-15 | 20 | Ireland, WIT | 100mH, 400m, 400mH, 4x200m, 4x400m, 60m, 60mH, CE, HJ, LJ, SP |
| Ella O Connor | f | 2023-11-10 | 2024-04-06 | 5 | UG | 800m, Road, XC |
| Meabh O Connor | f | 2024-02-10 | 2024-04-06 | 2 | SETU | 1500mW |
| Vanessa O Connor | f | 2016-11-19 | 2016-11-19 | 1 | TCD | Road |
| Naoise O Donnell | f | 2022-11-11 | 2024-02-10 | 5 | UG | 3000m, Road, XC |
| Aisling O Flynn | f | 2017-02-10 | 2018-04-14 | 5 | DCU | CE, HJ, LJ, SP |
| Aisling O Flynn | f | 2023-04-21 | 2024-02-10 | 7 | TCD | 100m, 200m, 4x100m, 4x200m |
| Ellen O Hanlon | f | 2016-11-19 | 2016-11-19 | 1 | TCD | Road |
| Abigale O Keeffe | f | 2019-03-02 | 2019-03-02 | 1 | UG | XC |
| Helena O Keeffe | f | 2022-11-11 | 2024-04-06 | 10 | UL | 1500m, 3000m, 800m, Road, XC |
| Sarah O Keeffe | f | 2019-02-08 | 2020-02-15 | 11 | IT Tralee | 60mH, CE, HJ, LJ, SP |
| Sarah O Keeffe | f | 2022-01-29 | 2022-01-29 | 4 | IT Tralee | CE, HJ, LJ, SP |
| Sadbh O Loan | f | 2019-11-16 | 2019-11-16 | 1 | UCD | Road |
| Bebhinn Ó Meadhra | f | 1970-03-14 | 1970-03-14 | 1 | TCD | XC |
| Laoise Ó Murchú | f | 1994-01-21 | 1994-04-23 | 4 | UCD | 400m, 400mH |
| Ciara O Neill | f | 2023-11-10 | 2024-02-10 | 3 | MTU | 3000m, Road |
| Nollaigh O Neill | f | 2021-11-13 | 2021-11-13 | 1 | CIT | Road |
| Lily O Riordan | f | 2024-02-10 | 2024-04-06 | 6 | MTU | 4x400m, 60mH, CE, HJ, LJ, SP |
| Emily O Shea | f | 2024-02-10 | 2024-04-06 | 5 | SETU | 4x200m, 800m, Mixed 4x400m |
| Aoife O Sullivan | f | 2022-01-29 | 2022-04-09 | 3 | CIT | 4x100m, HJ |
| Aoife O Sullivan | f | 2023-01-28 | 2024-04-06 | 7 | GST, MTU | 4x100m, 4x200m, HJ |
| Orla O Sullivan | f | 2024-04-05 | 2024-04-06 | 2 | MTU | 100m, 200m |
| Sive O Toole | f | 2022-01-29 | 2024-04-06 | 12 | UCD | 100m, 4x100m, 60m |
| Kate O`Connell | f | 2023-11-28 | 2023-11-28 | 1 | DCU | 300m |
| Una O' Brien | f | 2022-11-11 | 2022-11-11 | 1 | UCC | Road |
| Iseult O' Donnell | f | 2017-02-10 | 2018-03-10 | 5 | TCD | 400m, 4x200m, XC |
| Clodagh O' Mahoney | f | 2017-02-10 | 2017-05-27 | 8 | IUAA, UL | 400m, 400mH, 4x100m, 4x200m, 60mH |
| Niamh O'Boyle | f | 2002-02-16 | 2010-03-13 | 12 | TCD | 5000m, Road, XC |
| Ailish O'Brien | f | 1989-05-05 | 1994-06-28 | 18 | IUAA, UCC | DT, HT, SP |
| Aisling O'Brien | f | 2003-11-22 | 2003-11-22 | 1 | DIT | Road |
| Aisling O'Brien | f | 2007-04-13 | 2010-04-24 | 16 | TCD | 200m, 400m, 4x100m, 4x200m, 4x400m, JT, PV, Road |
| Aoife O'Brien | f | 2018-11-17 | 2022-04-09 | 11 | Ireland, UG | 1500m, 3000mSC, Road, XC |
| Cathy O'Brien | f | 1999-03-06 | 1999-11-13 | 5 | IUAA, TCD | 4x400m, 800m, Road, XC |
| Cathy O'Brien | f | 1996-12-13 | 1996-12-14 | 1 | WIT | 4x200m |
| Eimear O'Brien | f | 2002-11-16 | 2006-11-18 | 12 | GST, UCD | 5000m, Road, XC |
| Eimear O'Brien | f | 2011-11-12 | 2013-04-13 | 8 | UL | 1500m, 3000m, 5000m, Road, XC |
| Eimeir O'Brien | f | 2007-02-24 | 2007-04-14 | 2 | UCD | 3000m, XC |
| Eimer O'Brien | f | 2016-04-15 | 2016-04-16 | 1 | GST | 1500m |
| Emer O'Brien | f | 2022-11-11 | 2023-03-04 | 3 | DCU | 800m, Road, XC |
| Emer O'Brien | f | 2004-11-20 | 2005-04-23 | 4 | UCD | 3000m, 5000m, Road, XC |
| Emma O'Brien | f | 2018-11-17 | 2021-09-26 | 5 | DCU | 1500m, 3000m, Road, XC |
| Fiona O'Brien | f | 1995-02-10 | 1999-11-13 | 14 | IUAA, NUIM, SPM | 400m, 4x400m, 800m, Road, XC |
| Katie O'Brien | f | 1996-12-13 | 1996-12-14 | 1 | WIT | 400m |
| M. O'Brien | f | 1978-05-05 | 1981-05-02 | 8 | UCG | 100mH, 200m, LJ |
| M. O'Brien | f | 1967-06-01 | 1967-06-01 | 1 | TCD | 880y |
| M. O'Brien | f | 1979-05-04 | 1980-05-03 | 2 | UCC | 1500m |
| Mary O'Brien | f | 1979-03-17 | 1980-05-03 | 4 | UCC | 3000m, XC |
| Meabh O'Brien | f | 2016-04-15 | 2016-04-16 | 1 | IT Carlow | 4x100m |
| N. O'Brien | f | 1967-02-18 | 1967-02-18 | 1 | UCD | XC |
| Niamh O'Brien | f | 1966-05-07 | 1968-05-11 | 7 | UCD | 440y, 880y, DT |
| Norah O'Brien | f | 2018-11-17 | 2018-11-17 | 1 | UL | Road |
| Norah O'Brien | f | 2019-11-16 | 2021-11-13 | 4 | UL | Road, XC |
| Orlaith O'Brien | f | 2018-04-13 | 2020-02-15 | 5 | Ireland, WIT | 20lbWfD, JT, SP |
| Orlaith O'Brien | f | 2022-04-08 | 2022-04-09 | 1 | IT Carlow | JT |
| R O'Brien | f | 2022-11-11 | 2023-03-04 | 2 | UCD | Road, XC |
| R. O'Brien | f | 1978-05-05 | 1981-05-02 | 7 | NCPE, TCE | HJ, JTo |
| S. O'Brien | f | 1971-02-20 | 1972-03-04 | 2 | UCD | XC |
| Saoirse O'Brien | f | 2023-11-10 | 2023-11-10 | 1 | UCD | Road |
| Shauna O'Brien | f | 2004-02-06 | 2004-02-07 | 6 | UCD | 200m, 4x200m, 60m |
| Sheena O'Brien | f | 1966-02-19 | 1971-05-12 | 37 | UCD | 100y, 200m, 220y, 440y, 4x100m, 4x110y, DT, JTo, SP, XC |
| Shona O'Brien | f | 2019-02-08 | 2023-04-22 | 11 | UCC | 1500m, 4x400m, 800m, Road, XC |
| Siobhan O'Brien | f | 1989-05-05 | 1993-02-12 | 16 | UCC | 100m, 200m, 400m, 60m, LJ, SP |
| Steffanie O'Brien | f | 2002-04-19 | 2002-04-20 | 3 | TCD | DT, HT, SP |
| Veronika O'Brien | f | 2013-02-01 | 2013-02-01 | 1 | IT Carlow | 1500m |
| Vita O'Brien | f | 2023-11-10 | 2023-11-10 | 1 | TCD | Road |
| Aisling O'Briene | f | 2009-04-24 | 2009-04-25 | 1 | TCD | JT |
| Lara O'Byrne | f | 2020-02-15 | 2024-04-06 | 9 | TCD | 100mH, HJ, LJ, SP |
| Lauren O'Byrne | f | 2017-11-18 | 2017-11-18 | 1 | UCD | Road |
| P. O'Byrne | f | 1977-03-12 | 1977-03-12 | 1 | UCG | XC |
| Paula O'Byrne | f | 2013-03-09 | 2013-03-09 | 1 | DCU | XC |
| Sheila O'Byrne | f | 2017-11-18 | 2019-11-16 | 6 | MU | 1500m, 5000m, Road |
| Síle O'Byrne | f | 2015-11-14 | 2017-04-08 | 3 | MU | 1500m, Road |
| Anna O'Callaghan | f | 2023-03-04 | 2023-03-04 | 1 | UCC | XC |
| Brigid O'Callaghan | f | 2002-03-09 | 2002-03-09 | 1 | UCC | XC |
| Edel O'Callaghan | f | 1997-12-12 | 2000-02-26 | 7 | DIT | 200m, 4x400m, 800m, XC |
| N. O'Callaghan | f | 1981-05-01 | 1983-05-07 | 6 | UCD | 100mH, 400mH, HJ, LJ |
| Patrica O'Callaghan | f | 1999-06-22 | 2004-04-17 | 6 | NI U23, UU | 1500m, 3000m, 5000m, Road, XC |
| Laura O'Callahan | f | 2007-11-17 | 2007-11-17 | 1 | CIT | Road |
| Nicola O'Callaigh | f | 2008-11-15 | 2012-03-10 | 6 | UL | 3000m, Road, XC |
| Alannah O'Carroll | f | 2018-04-13 | 2018-04-14 | 2 | NCI | 200m, PV |
| Catherine O'Carroll | f | 1998-04-24 | 1998-04-25 | 3 | UCC | 400m, 4x100m |
| Catherine O'Carroll | f | 1999-03-06 | 1999-03-06 | 1 | CIT | XC |
| Dearbhla O'Carroll | f | 1991-03-02 | 1991-03-02 | 1 | SPM | XC |
| Moya O'Carroll | f | 1965-05-19 | 1966-05-18 | 6 | UCD | 100y, 220y, 4x110y, XC |
| A. O'Connell | f | 1969-05-15 | 1972-05-10 | 3 | TCD | 800m, 880y |
| Casie O'Connell | f | 2018-11-17 | 2018-11-17 | 1 | MU | Road |
| Corina O'Connell | f | 1997-04-25 | 1997-04-26 | 1 | DCU | JTo |
| Emer O'Connell | f | 2008-11-15 | 2011-02-05 | 15 | UCC | 12, 4, 8, 16, 400m, 4x200m, 4x400m, Road |
| Fiona O'Connell | f | 2010-04-23 | 2010-04-24 | 1 | UCC | 4x100m |
| Justyne O'Connell | f | 1998-02-28 | 1998-02-28 | 1 | UCD | XC |
| Kate O'Connell | f | 2024-02-10 | 2024-04-06 | 7 | DCU | 400m, 4x100m, 4x200m |
| Laura O'Connell | f | 2002-04-19 | 2002-04-20 | 2 | CIT | 1500m, HJ |
| M. O'Connell | f | 1972-05-05 | 1972-05-06 | 1 | UCG | 800m |
| Maire O'Connell | f | 2000-02-26 | 2000-02-26 | 1 | UCC | XC |
| Marie O'Connell | f | 2000-04-14 | 2003-04-26 | 15 | IUAA, UCC | 100mH, 400m, 400mH, 4x400m, CE, HJ, HT, LJ, SP, TJ |
| Mary O'Connell | f | 2010-11-13 | 2010-11-13 | 1 | TCD | Road |
| Maureen O'Connell | f | 1971-02-20 | 1975-03-08 | 6 | UCG | 1500m, 800m, XC |
| Moya O'Connell | f | 2024-02-10 | 2024-04-06 | 7 | DCU | 100mH, 400mH, 4x100m, 4x400m, 60mH |
| Stephanie O'Connell | f | 1986-05-02 | 1989-05-06 | 5 | QUB | 100m, 100mH, 200m |
| Susan O'Connell | f | 2010-11-13 | 2010-11-13 | 1 | UG | Road |
| O'Connor | f | 2022-11-11 | 2022-11-11 | 1 | UCD | Road |
| Aine O'Connor | f | 2019-03-02 | 2021-11-13 | 3 | TCD | 3000m, Road, XC |
| Aine O'Connor | f | 2023-11-10 | 2024-03-09 | 2 | UCD | Road, XC |
| Aoife O'Connor | f | 1995-02-10 | 1997-02-01 | 8 | UCC | 10000m, 3000m, 5000m, XC |
| Aoife O'Connor | f | 2011-11-12 | 2015-04-11 | 13 | UCD | 1500m, 3000m, 3000mSC, Road, XC |
| Brigid O'Connor | f | 1972-03-04 | 1975-05-03 | 9 | UCG | 1500m, 3000m, XC |
| C. O'Connor | f | 1968-05-11 | 1969-05-15 | 5 | UCD | 880y, HJ, XC |
| Claire O'Connor | f | 1993-06-22 | 2000-06-20 | 48 | IUAA, NI U20, QUB | 100m, 200m, 4x100m, 4x400m, 60m |
| Clare O'Connor | f | 2023-11-10 | 2024-04-06 | 6 | TUD | 1500m, 800m, Mixed 4x400m, Road, XC |
| Cliodhna O'Connor | f | 2017-11-18 | 2018-04-14 | 2 | UCD | 4x400m, Road |
| Deirdre O'Connor | f | 1996-12-13 | 1998-02-28 | 3 | UCG, UG | 1500m, XC |
| Deirdre O'Connor | f | 1997-12-12 | 1998-04-25 | 3 | IT Tralee | DT, JTo, SP |
| Eimear O'Connor | f | 2016-11-19 | 2020-03-07 | 10 | UCD | 3000m, 5000m, Road, XC |
| Jane O'Connor | f | 2005-02-26 | 2005-02-26 | 1 | UCC | XC |
| Jean O'Connor | f | 1999-03-06 | 2000-04-15 | 7 | UG | 1500m, 3000m, Road, XC |
| Karen O'Connor | f | 2008-04-18 | 2009-04-25 | 2 | UCC | DT |
| Kate O'Connor | f | 1997-02-01 | 2002-02-16 | 29 | DIT, Dublin Colleges, GST, IUAA, TCD | 1500m, 1500mW, 4x100m, 4x400m, 800m, Road, XC |
| Lesley O'Connor | f | 2000-12-01 | 2005-04-23 | 56 | IUAA, TCD | 100m, 100mH, 400m, 400mH, 4x100m, 4x200m, 4x400m, 60m, 60mH, 800m, CE, HJ, JT, LJ, PV, Road, SP |
| M. O'Connor | f | 1972-03-04 | 1972-03-04 | 1 | UCC | XC |
| Maeve O'Connor | f | 2014-11-15 | 2020-03-07 | 8 | UCD | Road, XC |
| Maeve O'Connor | f | 2019-03-02 | 2019-03-02 | 1 | UCD | XC |
| Margaret O'Connor | f | 1971-05-07 | 1971-05-08 | 1 | UCC | 4x100m |
| Margaret O'Connor | f | 2003-03-09 | 2003-03-22 | 2 | CIT, GST | XC |
| Margeurite O'Connor | f | 2006-12-02 | 2007-04-14 | 5 | UL | 100m, 200m, 60m, LJ, TJ |
| Marguerite O'Connor | f | 2008-04-18 | 2009-04-25 | 14 | UL | 100m, 200m, 4x100m, 4x200m, 60m, 60mH, CE, HJ, LJ, PV, SP, TJ |
| Maritta O'Connor | f | 1999-04-23 | 1999-04-24 | 1 | WIT | 4x100m |
| Marritta O'Connor | f | 1999-04-23 | 1999-04-24 | 2 | WIT | 4x100m, 4x400m |
| Martina O'Connor | f | 2020-03-07 | 2020-03-07 | 1 | GMIT | XC |
| Mary O'Connor | f | 1998-12-11 | 2002-04-20 | 15 | UCC | 200m, 400m, 4x200m, 4x400m, 800m, Road, XC |
| Mary O'Connor | f | 1999-11-13 | 1999-11-13 | 1 | UL | Road |
| Mary O'Connor | f | 1994-01-21 | 1994-01-21 | 3 | UCC | 60m, LJ |
| Megan O'Connor | f | 2016-02-12 | 2016-02-12 | 1 | TCD | PV |
| Monica O'Connor | f | 2011-04-29 | 2014-04-12 | 7 | UG | 400m, 4x200m |
| Niamh O'Connor | f | 2018-02-09 | 2019-02-08 | 3 | MU | 1500mW |
| Orla O'Connor | f | 2018-11-17 | 2018-11-17 | 1 | WIT | Road |
| Rachel O'Connor | f | 2013-04-12 | 2014-04-12 | 5 | ITB | 100m, 60m, LJ |
| Regina O'Connor | f | 1994-01-21 | 1994-01-21 | 2 | UCG | 60m, LJ |
| Rosemary O'Connor | f | 1980-03-01 | 1983-03-12 | 4 | UCG | XC |
| Sarah O'Connor | f | 2021-11-13 | 2021-11-13 | 1 | UCD | Road |
| Sarah O'Connor | f | 2023-01-28 | 2023-01-28 | 1 | QUB | 200m |
| Sinead O'Connor | f | 2015-02-06 | 2018-04-14 | 9 | DIT | 1500mW, Road |
| Sinead O'Connor | f | 2012-02-04 | 2016-04-16 | 36 | CIT, IUAA | 100mH, 200m, 4x100m, 4x200m, 4x400m, CE, HJ, LJ, PV, SP, TJ |
| Sinead O'Connor | f | 2011-11-12 | 2015-04-11 | 13 | UCC | 3000m, 5000m, Road, XC |
| Siobhan O'Connor | f | 2000-02-26 | 2001-04-21 | 5 | Dublin Colleges, RCSI | 1500m, 5000m, XC |
| Suzanne O'Connor | f | 2006-03-04 | 2006-03-04 | 1 | UCC | XC |
| Mary O'Conor | f | 2000-02-26 | 2000-02-26 | 1 | UCC | XC |
| Aoife O'Cuill | f | 2019-11-16 | 2024-02-10 | 10 | DCU | 3000m, 5000m, Road, XC |
| Kate O'Day | f | 1997-02-01 | 1997-02-01 | 1 | UCG | XC |
| Maura O'Dea | f | 2009-11-14 | 2012-03-10 | 6 | UCD | 800m, Road, XC |
| Michelle O'Dea | f | 2018-02-09 | 2019-05-25 | 4 | AIT, Ireland | DT, TJ |
| Michelle O'Dea | f | 2019-02-08 | 2019-04-06 | 5 | AIT | 4x100m, 4x200m, 60m, DT |
| C O'Doherty | f | 1994-01-21 | 1994-01-21 | 1 | UCG | SP |
| Emma O'Doherty | f | 2002-12-06 | 2006-04-22 | 29 | UG | 100mH, 4x100m, 4x400m, 60m, 60mH, CE, HJ, LJ, SP, TJ |
| Maura O'Doherty | f | 2001-11-07 | 2001-11-07 | 1 | UCD | Road |
| Siobhán O'Doherty | f | 2003-04-25 | 2007-03-31 | 14 | IUAA, UL | 1500m, 3000m, 5000m, 800m, Road, XC |
| Siobhon O'Doherty | f | 2003-11-22 | 2005-02-26 | 5 | UL | 1500m, 3000m, Road, XC |
| Aine O'Donnell | f | 2014-04-11 | 2014-04-12 | 1 | WIT | 5000m |
| Ann O'Donnell | f | 1976-04-30 | 1980-03-01 | 3 | UCG | 100m, 200m, XC |
| Breda O'Donnell | f | 1997-12-12 | 1997-12-13 | 2 | IT Tralee | 1500m, 3000m |
| Carol O'Donnell | f | 2014-02-07 | 2014-02-07 | 2 | AIT | 20lbWfD, SP |
| Grace O'Donnell | f | 2023-03-04 | 2024-03-09 | 2 | UL | XC |
| Iseult O'Donnell | f | 2012-11-17 | 2013-04-13 | 3 | TCD | 4x400m, 800m, Road |
| Isulet O'Donnell | f | 2012-07-18 | 2012-07-18 | 1 | Raheny Shamrocks AC | 800m |
| Keara M.B. O'Donnell | f | 1981-03-07 | 1981-03-07 | 1 | TCD | XC |
| Mary O'Donnell | f | 2023-03-04 | 2023-03-04 | 1 | UL | XC |
| Roisin O'Donnell | f | 2022-01-29 | 2022-01-29 | 2 | TUD | LJ, TJ |
| Sheila M. O'Donnell | f | 1982-03-06 | 1982-03-06 | 1 | TCD | XC |
| Una O'Donnell | f | 2024-02-10 | 2024-04-06 | 2 | UCD | HT, SP |
| Holly O'Donnell-Anderson | f | 2007-11-17 | 2008-11-15 | 6 | QUB | 1500m, 4x200m, 800m, Road |
| M. O'Donnellan | f | 1979-05-04 | 1980-05-03 | 3 | UCG | 100m, 200m |
| Amy O'Donoghue | f | 2014-03-08 | 2017-11-18 | 13 | IUAA, UL | 1500m, 4x400m, Road, XC |
| Brenda O'Donoghue | f | 2004-04-16 | 2004-04-17 | 2 | WIT | 1500mW, 5000m |
| Caitriona O'Donoghue | f | 1996-04-19 | 1998-04-25 | 3 | TCD | 1500m, 800m, LJ |
| Caitriona O'Donoghue | f | 2010-04-07 | 2010-04-07 | 2 | UCD | 1500m, 800m |
| Claire O'Donoghue | f | 1999-04-23 | 1999-04-24 | 1 | UL | 5000m |
| Elaine O'Donoghue | f | 1997-12-12 | 2001-04-21 | 12 | UL | 1500m, 3000m, 5000m, Road, XC |
| Katie O'Donoghue | f | 2014-02-07 | 2014-02-07 | 4 | UG | CE, HJ, LJ, SP |
| Niamh O'Donoghue | f | 2014-03-08 | 2015-04-11 | 11 | CIT | 100mH, CE, HJ, LJ, SP, XC |
| Orna O'Donoghue | f | 1998-12-11 | 1998-12-12 | 3 | UL | 4x200m, 60mH |
| Catrina O'Donohoe | f | 1995-12-16 | 2001-04-21 | 16 | TCD | 1500m, 4x200m, 800m, LJ, Road, XC |
| Ann Marie O'Donovan | f | 1994-01-21 | 1994-01-21 | 1 | UCD | 200m |
| Toni O'Donovan | f | 1997-02-01 | 1998-02-28 | 2 | UL | XC |
| Ciara O'Dowd | f | 2011-04-29 | 2011-04-30 | 1 | UG | 1500mW |
| Laura O'Dowd | f | 2013-02-01 | 2015-03-07 | 11 | AIT | 1500m, 4x100m, 4x200m, 4x400m, 800m, Road, SP, XC |
| A. O'Driscoll | f | 1970-03-14 | 1970-03-14 | 1 | UCG | XC |
| A. O'Driscoll | f | 1969-05-03 | 1969-05-15 | 4 | UCD | 220y, HJ, LJ |
| A. O'Driscoll | f | 1968-05-11 | 1970-05-09 | 7 | UCG | 100mH, 100y, 200m, 440y, 4x100m, LJ |
| Aileen O'Driscoll | f | 2011-11-12 | 2011-11-12 | 1 | TCD | Road |
| E. O'Driscoll | f | 1970-03-14 | 1970-03-14 | 1 | UCC | XC |
| E. O'Driscoll | f | 1974-05-03 | 1974-05-04 | 1 | NCPE | DT |
| E. O'Driscoll | f | 1975-05-21 | 1977-05-17 | 7 | UCD | 800m, DT, HJ, LJ, SP, XC |
| E. O'Driscoll | f | 1977-05-06 | 1977-05-07 | 1 | QUB | DT |
| Laura O'Driscoll | f | 2011-03-12 | 2011-03-12 | 1 | UL | XC |
| Ailbhe O'Driscoll Collins | f | 2008-04-18 | 2008-04-19 | 1 | UCC | 400m |
| Dympna O'Dwyer | f | 2008-04-18 | 2014-03-08 | 12 | UG | 1500m, 3000m, Road, XC |
| Dympna O'Dwyer | f | 2014-02-07 | 2014-02-07 | 1 | UG | 3000m |
| Martina O'Dwyer | f | 2012-03-10 | 2012-03-10 | 1 | WIT | XC |
| Noreen O'Dwyer | f | 2001-12-07 | 2005-04-23 | 25 | IUAA, UCC | 20lbWfD, DT, HT, JT, SP |
| Aine O'Farrell | f | 2018-11-17 | 2023-04-22 | 12 | UL | 3000m, 3000mSC, Road, XC |
| Charlotte O'Farrell | f | 2010-04-23 | 2012-04-21 | 7 | GST, WIT | 20lbWfD, HT, SP |
| Kerry O'Flaherty | f | 1999-06-22 | 2003-04-26 | 4 | NI U23, UU | 3000m, 4x400m, 800m, XC |
| L. O'Flynn | f | 1986-03-08 | 1986-03-08 | 1 | UCC | XC |
| Suzie O'Flynn | f | 2019-11-16 | 2021-11-13 | 2 | DCU | Road |
| Fiona O'Friel | f | 2003-04-25 | 2009-04-25 | 26 | IUAA, TCD, UCD | 100m, 12, 4, 8, 16, 200m, 4x100m, 4x200m, 4x400m, 60m, LJ, SP |
| Helen O'Friel | f | 1988-02-01 | 1988-02-01 | 1 | UCD | Road |
| Fiona O'Frighill | f | 2001-12-07 | 2002-06-18 | 14 | IUAA, UCD | 100m, 200m, 4x100m, 4x200m, 60m, LJ |
| Aine O'Gorman | f | 2014-11-15 | 2015-02-21 | 2 | TCD | Road, XC |
| Pat O'Grady | f | 1991-03-02 | 1991-03-02 | 1 | UL | XC |
| Catherine O'Hagan | f | 1996-02-09 | 1996-12-14 | 2 | UL | 60mH |
| Patricia O'Hagan | f | 2012-07-18 | 2012-07-18 | 1 | St Peters Lurgan | 800m |
| A. O'Halloran | f | 1976-03-06 | 1976-03-06 | 1 | SPM | XC |
| A. O'Halloran | f | 1980-03-01 | 1980-03-01 | 1 | UCG | XC |
| Margaret O'Halloran | f | 1996-04-19 | 1998-06-23 | 10 | IUAA, UCC, UCD | 100m, 200m, 4x100m, 60m, PV |
| Margaret O'Halloran | f | 2000-12-01 | 2000-12-02 | 1 | UCD | PV |
| Michelle O'Halloran | f | 1995-12-16 | 1995-12-16 | 1 | NUIM | XC |
| E. O'Hanlon | f | 1974-05-03 | 1976-05-01 | 3 | NCPE | DT, SP |
| Ellen O'Hanlon | f | 2014-11-15 | 2014-11-15 | 1 | TCD | Road |
| Karen O'Hanlon | f | 1991-03-02 | 1991-03-02 | 1 | UU | XC |
| Roisin O'Hanlon | f | 2013-04-12 | 2014-04-12 | 2 | IT Tallaght | 1500m |
| Theresa O'Hanlon | f | 2001-04-07 | 2003-04-26 | 6 | UL | 3000m, 5000m, Road, XC |
| Emma O'Hanlon-Geary | f | 2018-11-17 | 2019-04-06 | 2 | IT Carlow | 3000mSC, Road |
| Kim O'Hare | f | 2019-02-08 | 2023-04-22 | 11 | DCU | CE, HJ, LJ, SP, TJ |
| Niamh O'Hare | f | 1994-01-21 | 1998-04-25 | 20 | IUAA, UL | 100m, 200m, 4x100m, 4x200m, 4x400m, 60m |
| Sorcha O'Higgins | f | 2009-11-14 | 2009-11-14 | 1 | UCD | Road |
| Lilly-Ann O'Hora | f | 2011-04-29 | 2018-04-14 | 18 | DCU, GST, IUAA | 100m, 100mH, 400mH, 4x100m, 60m, 60mH |
| Lilly-Ann O'Hora | f | 2019-04-05 | 2019-04-06 | 1 | GST | 100mH |
| Roisin O'Kane | f | 2012-07-18 | 2012-07-18 | 1 | Ballymena & Antrim AC | DT |
| Sinéad O'Kane | f | 2009-02-14 | 2010-02-13 | 3 | NUIM | 200m, LJ |
| Anne O'Kearney Flynn | f | 1985-05-03 | 1986-03-08 | 2 | UCC | 3000m, XC |
| Katherine O'Keefe | f | 2016-03-05 | 2019-03-02 | 15 | IUAA, UL | 1500m, 3000m, 4x400m, 800m, Road, XC |
| Lucy O'Keefe | f | 2022-03-05 | 2022-03-05 | 1 | UCC | XC |
| T. O'Keefe | f | 1989-05-05 | 1989-05-06 | 1 | TCE | JT |
| Dervla O'Keeffe | f | 1999-12-03 | 2001-04-21 | 4 | TCD | 1500mW, DT, JT, SP |
| E. O'Keeffe | f | 1989-03-04 | 1989-03-04 | 1 | UCC | XC |
| Eileen O'Keeffe | f | 2001-04-20 | 2009-04-25 | 33 | AIT, IUAA, RCSI | 20lbWfD, DT, HT, JT, SP |
| H. O'Keeffe | f | 1990-04-27 | 1990-04-28 | 1 | SPM | 1500mW |
| M. O'Keeffe | f | 1980-03-01 | 1980-03-01 | 1 | UCC | XC |
| M. O'Keeffe | f | 1989-03-04 | 1989-03-04 | 1 | UCC | XC |
| Margaret O'Keeffe | f | 1986-03-08 | 1989-03-04 | 4 | SPM | 1500mW, XC |
| Serena O'Keeffe | f | 2000-12-01 | 2004-04-17 | 6 | TCD | 1500mW, XC |
| Siobhán O'Keeffe | f | 1993-02-12 | 1996-04-20 | 5 | UL | 3000m, 800m, XC |
| Siobhan O'Keeffe | f | 2000-04-14 | 2000-04-15 | 1 | UL | HT |
| A. O'Leary | f | 1981-03-07 | 1981-03-07 | 1 | UCC | XC |
| Ann O'Leary | f | 1981-05-01 | 1983-05-07 | 4 | UCC | 100m, 200m, 400mH |
| Anne O'Leary | f | 1999-11-13 | 2001-04-21 | 7 | UL | 1500m, 1500mW, 3000m, Road, XC |
| Eimear O'Leary | f | 2013-11-23 | 2013-11-23 | 1 | UG | Road |
| Helen O'Leary | f | 1997-12-12 | 1998-04-25 | 5 | TCD | 200m, 400m, 4x100m |
| Joy O'Leary | f | 2013-11-23 | 2014-04-12 | 4 | CIT | 4x100m, 4x400m, Road, XC |
| Sinead O'Leary | f | 1996-12-13 | 1996-12-14 | 2 | WIT | 1500m, 800m |
| Jenny O'Loughlin | f | 2013-11-23 | 2016-04-16 | 5 | WIT | 3000m, 5000m, 800m, Road, XC |
| Emily O'Mahoney | f | 2022-01-29 | 2022-04-09 | 3 | WIT | LJ, TJ |
| J. O'Mahoney | f | 1980-03-01 | 1980-03-01 | 1 | UCG | XC |
| Orla O'Mahoney | f | 1997-04-25 | 1999-12-04 | 10 | UCD | 1500m, 3000m, 4x200m, 4x400m, 5000m, 800m |
| C. O'Mahony | f | 1979-05-23 | 1979-05-23 | 1 | UCD | 1500m |
| E. O'Mahony | f | 1995-02-10 | 1995-02-10 | 1 | UL | HJ |
| N. O'Mahony | f | 1980-05-02 | 1980-05-03 | 1 | UCD | LJ |
| Niamh O'Mahony | f | 2021-11-13 | 2022-04-09 | 4 | UCC | 3000m, 5000m, Road, XC |
| Orla O'Mahony | f | 1997-02-01 | 2002-04-20 | 15 | IUAA, UCD | 1500m, 3000m, Road, XC |
| Aoife O'Malley | f | 2006-12-02 | 2013-04-13 | 23 | UL | DT, JT, LJ, SP, TJ |
| Edwina O'Malley | f | 2005-04-22 | 2005-04-23 | 1 | RCSI | 100m |
| Siobhán O'Malley | f | 1997-12-12 | 1998-04-25 | 7 | WIT | 1500mW, DT, HT, JTo, SP |
| C. O'Maloney | f | 1979-03-17 | 1979-03-17 | 1 | UCD | XC |
| Claire O'Meara | f | 2003-02-15 | 2003-11-22 | 3 | UCD | Road, XC |
| Edel O'Meara | f | 2001-12-07 | 2009-04-25 | 14 | UG, UU | 4x200m, PV |
| Marie O'Meara | f | 1992-01-31 | 1996-06-25 | 55 | IUAA, TCD, UL | 100mH, 200m, 400mH, 4x200m, 60m, 60mH, CE, HJ, JT, LJ, SP, TJ |
| Una O'Mhurchu | f | 2000-04-14 | 2000-04-15 | 1 | UCD | PV |
| Una O'Mhurica | f | 2000-04-14 | 2000-04-15 | 1 | UCD | HJ |
| B. O'Mullin | f | 1970-03-14 | 1970-03-14 | 1 | QUB | XC |
| Una O'Murchu | f | 2000-04-14 | 2000-04-15 | 1 | UCD | 200m |
| Abbie O'Neill | f | 2024-02-10 | 2024-02-10 | 1 | QUB | PV |
| Aideen O'Neill | f | 2011-11-12 | 2011-11-12 | 1 | UCC | Road |
| Arlene O'Neill | f | 2011-03-05 | 2013-06-01 | 19 | GST, IUAA, TCD | 100m, 200m, 20lbWfD, 3000mSC, 400m, 4x100m, 4x200m, 4x400m, 60m, XC |
| C. O'Neill | f | 1979-03-17 | 1980-05-14 | 7 | UCD | DT, SP, XC |
| Catherine O'Neill | f | 1993-06-22 | 1999-04-24 | 11 | IUAA, NI U20, QUB, Queen's Select | 1500m, 4x400m, 800m, XC |
| Catherine O'Neill | f | 2012-04-20 | 2012-04-21 | 2 | GST | DP, JC |
| Ciara O'Neill | f | 2018-02-09 | 2021-09-26 | 4 | UL | 3000m, XC |
| Doireann O'Neill | f | 1996-12-13 | 1996-12-14 | 2 | Tralee RTC | 400m, TJ |
| Eadaoin O'Neill | f | 2006-11-18 | 2008-03-08 | 2 | UL | Road, XC |
| Eadaoin O'Neill | f | 2012-03-10 | 2013-04-13 | 2 | UCC | 5000m, XC |
| Hannah O'Neill | f | 2023-01-28 | 2023-01-28 | 1 | TUD | 800m |
| Kathleen O'Neill | f | 2003-03-09 | 2003-03-09 | 1 | UCC | XC |
| Laurena O'Neill | f | 1996-02-09 | 1996-02-10 | 1 | UL | 400m |
| Laurna O'Neill | f | 1996-02-09 | 1996-02-10 | 1 | UL | 4x200m |
| Leah O'Neill | f | 2022-11-11 | 2023-03-04 | 2 | UCD | Road, XC |
| Lorna O'Neill | f | 1994-04-22 | 1997-02-01 | 6 | UL | 200m, 400m, XC |
| M. O'Neill | f | 1965-05-19 | 1968-05-11 | 5 | UCD | 100y, 4x110y, JTo, LJ |
| Mairead O'Neill | f | 2015-04-10 | 2017-05-27 | 8 | IUAA, UCD | 16lbWfD, 20lbWfD, HT |
| Mary O'Neill | f | 1983-03-12 | 1984-05-05 | 2 | UCC | 800m, XC |
| Niamh O'Neill | f | 2000-12-01 | 2004-04-17 | 17 | WIT | 200m, 400m, 4x100m, 4x200m, 60m, SP |
| Niamh O'Neill | f | 2017-04-07 | 2019-11-16 | 6 | UCD | 3000m, 5000m, Road, XC |
| Niamh O'Neill | f | 2022-01-29 | 2024-02-10 | 17 | DCU | 100m, 100mH, 4x100m, 4x200m, 60m, 60mH |
| Sarah O'Neill | f | 2022-01-29 | 2022-01-29 | 1 | QUB | 60mH |
| T. O'Neill | f | 1979-05-23 | 1980-05-14 | 3 | UCD | DT, JTo |
| M. O'Regan | f | 1978-05-05 | 1979-05-05 | 6 | NCPE, TCE | 100m, 200m, LJ |
| Rachel O'Regan | f | 2004-11-20 | 2004-11-20 | 1 | TCD | Road |
| Caoimhe O'Reilly | f | 2021-11-13 | 2023-11-10 | 4 | QUB | Road, XC |
| Catherine O'Reilly | f | 1988-04-29 | 1988-04-30 | 1 | TCD | 1500mW |
| Cora O'Reilly | f | 1996-02-17 | 2004-04-17 | 37 | IUAA, TCD | 1500m, 200m, 3000m, 400m, 4x400m, 5000m, 800m, Road, XC |
| Éadaoin O'Reilly | f | 2014-03-08 | 2014-04-12 | 2 | UU | 3000mSC, XC |
| K. O'Reilly | f | 1986-03-08 | 1986-03-08 | 1 | TCD | XC |
| Louise O'Reilly | f | 2007-11-17 | 2008-04-19 | 4 | TCD | 1500m, 3000m, Road, XC |
| Niamh O'Reilly | f | 1989-03-04 | 1992-04-25 | 5 | UCD | 1500mW, XC |
| Niamh O'Reilly | f | 2005-04-22 | 2005-12-11 | 3 | UCD | 400mH, 60mH |
| Orla O'Reilly | f | 2020-02-15 | 2020-02-15 | 3 | UCC | 200m, 4x200m |
| Róisín O'Reilly | f | 2021-11-13 | 2023-11-10 | 10 | UCD | 1500m, 1500mW, 3000mSC, Road, XC |
| Roisin O'Reilly | f | 2024-02-10 | 2024-02-10 | 2 | UCD | 1500m |
| Susan O'Reilly | f | 1994-04-22 | 1999-04-24 | 19 | UL | 200m, 400m, 4x100m, 4x200m, 60m, 800m, DT |
| Suzanne O'Reilly | f | 1996-02-09 | 1996-02-10 | 1 | UL | 400m |
| Therese O'Reilly | f | 1977-12-10 | 1978-03-04 | 2 | UCD | XC |
| Susan O'Reily | f | 1999-04-23 | 1999-04-24 | 3 | UL | 200m, 4x400m |
| Fiona O'Riardan | f | 2004-12-03 | 2005-04-23 | 9 | UCC | 4x100m, 4x400m, 60mH, 800m, CE, HJ, LJ, SP |
| Fiara O'Riordain | f | 2004-02-06 | 2004-02-07 | 3 | UCC | 400m, LJ, SP |
| L. O'Riordan | f | 1988-04-29 | 1988-04-30 | 2 | TCE | 200m, 400m |
| Laura O'Riordan | f | 2015-04-10 | 2015-04-11 | 1 | CIT | JT |
| Niamh O'Riordan | f | 2000-12-01 | 2002-04-20 | 7 | CIT, IUAA | JT, SP |
| Derval O'Rourke | f | 2001-04-20 | 2005-04-23 | 23 | UCD | 100m, 100mH, 200m, 20lbWfD, 4x100m, 4x200m, 60mH, LJ, SP |
| Niamh O'Rourke | f | 1990-03-03 | 1994-04-23 | 18 | UCC | 100mH, 400m, HJ, JT, JTo, LJ, SP, TJ, XC |
| Niamh O'Rourke | f | 2012-02-04 | 2013-04-13 | 5 | IT Carlow | 100m, 4x100m, 4x200m, 60m |
| Roisin O'Rourke | f | 1989-05-05 | 1990-03-03 | 6 | UCG | 200m, 400m, LJ, XC |
| Roisin O'Rourke | f | 1994-01-21 | 1994-04-23 | 4 | SPM | HJ, JT, LJ, SP |
| Megan O'Sadnick | f | 2007-11-17 | 2007-11-17 | 1 | UCC | Road |
| Caroline O'Shea | f | 1993-02-12 | 1993-02-12 | 2 | UL | 800m, HJ |
| Celine O'Shea | f | 2013-11-23 | 2016-04-16 | 10 | CIT | 400mH, 4x100m, 4x400m, 800m, CE, HJ, LJ, Road, SP |
| Fiona O'Shea | f | 2016-02-12 | 2016-02-12 | 2 | UL | LJ, TJ |
| Gillian O'Shea | f | 2001-11-07 | 2003-03-09 | 2 | UCD | Road, XC |
| Helen O'Shea | f | 2007-11-17 | 2009-03-07 | 3 | CIT | Road, XC |
| Katie O'Shea | f | 2007-12-08 | 2011-04-30 | 14 | UL | 20lbWfD, DT, HT, JT, SP |
| Keara O'Shea | f | 2001-11-07 | 2001-11-07 | 1 | UCC | Road |
| Linda O'Shea | f | 1999-04-23 | 1999-12-04 | 5 | IT Tralee | 100m, 1500m, 3000m, 800m |
| Lorraine O'Shea | f | 2013-02-01 | 2015-04-11 | 8 | DCU, IUAA | LJ, TJ |
| M. O'Shea | f | 1986-03-08 | 1986-03-08 | 1 | NIHED | XC |
| Muireann O'Shea | f | 2014-11-15 | 2015-04-11 | 2 | UCD | 3000m, Road |
| Noreen O'Shea | f | 2008-03-08 | 2008-03-08 | 1 | CIT | XC |
| Rachael O'Shea | f | 2013-02-01 | 2017-04-08 | 28 | CIT, IUAA | 1500m, 400m, 4x100m, 4x200m, 4x400m, 800m, Road, XC |
| S. O'Shea | f | 1990-03-03 | 1990-03-03 | 1 | SPM | XC |
| A. O'Sullivan | f | 1972-03-04 | 1972-05-06 | 2 | UCC | 1500m, XC |
| A. O'Sullivan | f | 1995-04-21 | 1995-04-22 | 1 | UCD | HJ |
| Alice O'Sullivan | f | 2005-12-10 | 2006-12-03 | 10 | UL | 4x200m, 60mH, HJ, LJ, Road, TJ |
| Aoife O'Sullivan | f | 2021-11-13 | 2022-03-05 | 2 | UCD | Road, XC |
| Brid O'Sullivan | f | 2003-04-25 | 2003-04-26 | 1 | IT Tralee | 1500m |
| Ciara O'Sullivan | f | 2014-02-07 | 2015-11-14 | 3 | UG | 3000m, Road, XC |
| Elain O'Sullivan | f | 2008-03-08 | 2008-03-08 | 1 | CIT | XC |
| Eleanor O'Sullivan | f | 2000-04-14 | 2000-12-02 | 2 | AIT | 1500m, 5000m |
| Elle O'Sullivan | f | 2001-04-20 | 2001-04-21 | 2 | AIT | 3000m, 800m |
| Fiona O'Sullivan | f | 1993-03-06 | 1994-04-23 | 4 | UCC | 10000m, JT, XC |
| Gillian O'Sullivan | f | 1995-04-21 | 1998-12-12 | 7 | UCC | 1500mW |
| Grainne O'Sullivan | f | 1994-01-21 | 1997-12-13 | 26 | UCC, UCD | 100m, 200m, 4x200m, 60m, CE, HJ, LJ, TJ |
| Hannah O'Sullivan | f | 2015-02-06 | 2017-04-08 | 7 | IUAA, UCC | 20lbWfD, DT, SP |
| Jennifer O'Sullivan | f | 2008-11-15 | 2011-03-12 | 4 | DCU | Road, XC |
| Johannah O'Sullivan | f | 2010-02-13 | 2010-02-13 | 1 | UL | 1500mW |
| Lucy O'Sullivan | f | 2011-11-12 | 2012-04-21 | 2 | TCD | 3000m, Road |
| M. O'Sullivan | f | 1977-03-12 | 1977-03-12 | 1 | NCPE | XC |
| Maria O'Sullivan | f | 2011-03-05 | 2014-05-31 | 14 | IUAA, TCD | 3000m, 5000m, Road, XC |
| Maria O'Sullivan | f | 2014-11-15 | 2015-11-14 | 6 | DCU | 3000m, 5000m, Road, XC |
| Mary Anne O'Sullivan | f | 2011-11-12 | 2015-04-11 | 18 | DCU | 1500m, 4x400m, 800m, Road, XC |
| Moira O'Sullivan | f | 2000-11-12 | 2000-11-12 | 1 | UCC | Road |
| N. O'Sullivan | f | 1983-05-06 | 1983-05-07 | 1 | NIHED | 3000m |
| V. O'Sullivan | f | 1983-03-12 | 1983-03-12 | 1 | UCC | XC |
| B. O'Toole | f | 1968-05-01 | 1972-05-10 | 19 | UCD | 100m, 100y, 200m, 400m, 440y, 4x100m, LJ |
| Cliona O'Toole | f | 2023-11-10 | 2023-11-10 | 1 | TCD | Road |
| Elaine O'Toole | f | 1997-12-12 | 1997-12-13 | 1 | UU | 200m |
| Ellie O'Toole | f | 2019-02-08 | 2022-04-09 | 12 | UG | 200m, 400m, 4x200m, 4x400m, 800m |
| Emma O'Toole | f | 2012-04-20 | 2014-04-12 | 14 | WIT | 100m, 200m, 4x100m, 4x200m, LJ |
| Grainne O'Toole | f | 1999-03-06 | 1999-04-24 | 2 | IT Carlow | 3000m, XC |
| Martina O'Toole | f | 2004-02-06 | 2004-04-17 | 3 | DCU | 4x100m, 4x200m |
| T. O'Toole | f | 1970-03-14 | 1970-03-14 | 1 | UCD | XC |
| Caroline Oakes | f | 2003-06-10 | 2004-06-08 | 3 | NI U23 | DT, JT |
| Isobel Oakes | f | 2018-11-17 | 2018-11-17 | 1 | IT Carlow | Road |
| Katrina Oakes | f | 2002-06-18 | 2002-06-18 | 1 | NI U23 | 3000m |
| Sharon Oakes | f | 2000-06-20 | 2000-06-20 | 2 | NI U23 | HJ, TJ |
| Deborah Ogah | f | 2024-02-10 | 2024-02-10 | 1 | MTU | 60m |
| Destiny Ogunmakinde | f | 2022-04-08 | 2022-04-09 | 1 | AIT | 1500mW |
| Destiny Ogunmakinde | f | 2024-04-05 | 2024-04-06 | 1 | TUS | 1500mW |
| Margaret ÓhÓgartaigh | f | 1994-02-19 | 1998-04-25 | 14 | GST, UCD | 10000m, 1500mW, 3000m, 400mH, 800m, PV, SP, XC |
| Ovuezienye Carissa Okoro | f | 2023-01-28 | 2023-01-28 | 1 | UCD | SP |
| Lola Olajide | f | 2012-02-04 | 2014-04-12 | 11 | IT Carlow | 100m, 4x100m, 4x200m, 60m, LJ |
| Shakirat Olayode | f | 2024-04-05 | 2024-04-06 | 1 | MU | JT |
| Cecile Ollagnier | f | 2001-11-07 | 2003-11-22 | 2 | TCD | Road |
| Aishat Onilogbo | f | 2020-02-15 | 2020-02-15 | 3 | UCC | 4x200m, 60m |
| Aishat Onilogbo | f | 2023-01-28 | 2024-04-06 | 6 | UCC | 4x100m, 4x200m, LJ, SP |
| Katie Ord | f | 2015-05-31 | 2018-05-26 | 10 | Scotland, SUCA | DT, HT, SP |
| Danielle Organ | f | 2021-11-13 | 2021-11-13 | 1 | UG | Road |
| Noa Orizales | f | 1999-11-13 | 2000-02-26 | 2 | UL | Road, XC |
| Kate Ormsby | f | 2024-02-10 | 2024-02-10 | 1 | UCD | 60mH |
| Aeyla Orr | f | 2024-02-10 | 2024-02-10 | 1 | UCD | LJ |
| Heather Orr | f | 1998-06-23 | 1999-06-22 | 4 | NI U23 | 100mH, 400mH, TJ |
| Julia Orr | f | 2007-03-31 | 2007-03-31 | 1 | SU | XC |
| Liz Orr | f | 1995-06-20 | 1996-06-25 | 4 | NI U23 | LJ, TJ |
| Suzanne Orr | f | 1996-06-25 | 1998-06-23 | 3 | SU | 100m, 200m |
| Sarah-Jane Osborne | f | 2002-12-06 | 2002-12-07 | 2 | TCD | 1500m, 60m |
| A.N. Other | f | 1965-05-19 | 2024-04-06 | 1811 | Birmingham, CIT, DCU, DIT, Dublin, GST, H & Y, IT Tralee, IUAA, Loughborough, Louvain, MU, NCPE, NI U20, NI U23, NIHED, NUIM, NUU, QUB, RCSI, SPM, SU, TCD, TCE, TUD, UCC, UCD, UCG, UG, UL, Unknown, UU, Waterford RTC, WIT | 100m, 100mH, 100y, 100yH, 1500m, 200m, 220y, 3000m, 400m, 440y, 4x100m, 4x100y, 4x110y, 4x200m, 4x400m, 800m, 80mH, 880y, DT, HJ, JT, JTo, LJ, Road, SP, XC |
| Nicole Ouellet | f | 2008-03-08 | 2008-03-08 | 1 | UG | XC |
| Jill Overend | f | 1999-06-22 | 2001-06-19 | 7 | SU | DT, HT, JT, SP |
| Emma Owens | f | 2017-02-10 | 2018-04-14 | 6 | DCU | 20lbWfD, DT, HT, SP |
| Emma Owens | f | 2013-04-12 | 2015-04-11 | 5 | DCU | DT, SP |