- Nyren
- O'Brian
- O'Brien
- O'Bryon
- Eliza (1807 - after 1871)
- O'Callaghan
- O'Connell
- O'Connor
- O'Donaghue
- O'Donnell
- O'Donoghue
- O'Driscoll
- O'Grady
- O'Hagan
- O'Hare
- O'Kane
- O'Keefe
- Julia (1880 - circa 1977)
- O'Malley
- Anne (between 1869 and 1870 - )
- O'Mara
- O'Neil
- O'Neill
- O'Rorke
- O'Shaughnessy
- O'Shea
- O'Sullivan
- Oakden
- Oakes
- Oakley
- Oakman
- Oates
- Oatley
- Oben
- Ann (between 1831 and 1832 - )
- Oberg
- Oberheim
- Oberlies
- Obey
- Ockenden
- Odd
- Dorcas (between 1827 and 1828 - circa 1902)
- James (before 1808 - )
- Sarah (before 1808 - )
- Sarah (1826 - circa 1894)
- Odeman
- Odemar
- Odman
- Oehlke
- Ogden
- Oglander
- Oke
- Okeover
- Jane (before 1565 - 1620)
- Oldaker