O
| Title | Date of creation | Surname | Current status | Notes |
|---|---|---|---|---|
| O'Brien of Leaghmenagh | 1686 | O'Brien | extant | fifth Baronet succeeded as Baron Inchiquin in 1855; Baronetcy dormant (eleventh Baron and ninth Baronet died 1982) |
| O'Connor of Sligo | 1622 | O'Connor | extinct 1625 | |
| O'Donnell of Newport House | 1780 | O'Donnell | extinct 1889 | |
| O'Neill of Killelagh | 1666 | O'Neill | forfeit 1691 | |
| O'Neill of Upper Claneboys | 1643 | O'Neill | dormant 1799 | |
| Osborne of Ballentaylor | 1629 | Osborne | extant |
Read more about this topic: List Of Baronetcies In The Baronetage Of Ireland