Agents persons, peoples and institutions
O'Prunty (Patrick) See: Pádraig Ó Pronntaigh
- d. 1980
O'Rahilly (Egan) See: Aogán Ó Rathaille
- d. 1953
- d. 1830
O'Reilly (Jennifer L.) See: Jennifer O'Reilly
- d. 2016
O'Roddy (Thaddeus) See: Tadhg Ó Rodaighe
- s. xx–xxi
- d. 1673
- d. 1984
O'Sullivan (Humphrey) See: Amhlaoibh Ó Súilleabháin
- s. xx–xxi
- d. 1634 or after
- Spain, Santiago de Compostella, Portugal