Claimants
- O'Beirne
- O'Boyle
- O'Brien
- O'Brien Hishon
- O'Brien Kelly
- O'Brien Smyth
- O'Bryen
- O'Byrne
- O'Callaghan
- O'Carroll
- O'Connell
- O'Connell Fitzsimon
- O'Connolly
- O'Connor
- O'Dea
- O'Doherty
- O'Donaghue
- O'Donahoe
- O'Donnell
- O'Donoghoe
- O'Donoghue
- O'Donohoe
- O'Donovan
- O'Dowd
- O'Driscoll
- O'Dwyer
- O'Farrell
- O'Flaherty
- O'Flynn
- O'Gara
- O'Gorman
- O'Grady
- O'Hagan
- O'Halloran
- O'Hanlon
- O'Hara
- O'Hart
- O'Hehir
- O'Kane
- O'Kearney
- O'Keeffe
- O'Kelly
- O'Kennedy
- O'Leary
- O'Looney
- O'Loughlin
- O'Mahony
- O'Malley
- O'Mara
- O'Meara
- O'Moore
- O'Morchoe
- O'Neill
- O'Regan
- O'Reilly
- O'Riordan
- O'Rourke
- O'Shaughnessy
- O'Shea
- O'Sullivan
- O'Sutton
- O'Toole
- Oakes
- Oakman Hume
- Oates
- Odbert
- Olden
- Oliver
- Olphert Gage Dougherty
- Oman
- Oragano
- Orchard
- Ormsby
- Orpen
- Orr
- Osborne
- Oulton
- Owen
- Owen Lewis
- Owen Wells
- Owens
- Owens Lemon
- Oxberry