O
O'Briensbridge, O'Callaghans Mills, Ogonnelloe, Oilgate, Old Leighlin, Oldcastle, Oldtown (Dublin), Old Town (Roscommon), Omeath, Ongar, Oola, Oranmore, Oughterard, Oulart, Ovens, Owenbeg, Oxmantown, Oysterhaven
Read more about this topic: List Of Populated Places In The Republic Of Ireland