O
- (Kerry) Oaghley
- (County Cork) O'Callagha Park
- (County Cork) Oldcastletown
- (County Waterford) Old Pike Bridge
- (County Tipperary) Oldgrange
- (County Tipperary) Oaklands
- (Limerick City and County Council) Oldtown
- (Limerick City and County Council) Old Bridge
- (Clare) Ogonnelloe
- (County Tipperary) Outeragh
- (County Tipperary) Orkneys Cross Roads
- (County Cork) Old Bride Bridge
- (Limerick City and County Council) Oolagh Bridge
- (Clare) Oughterard
- (Clare) Oldtown
- (Limerick City and County Council) Oldmill Bridge
- (Limerick City and County Council) Odell Ville
- (Clare) Oil Mill Bridge
- (Clare) Oatfield
- (Clare) O’Brien’s Bridge
- (Clare) Oughtdarra
- (Clare) Oughtmama
- (Kerry) Owgarrif Bridge
- (County Tipperary) Oakhampton
- (County Cork) Ovens
- (County Cork) Orthon Island
- (County Cork) Old Twopothouse Cross Roads
- (County Cork) Oldchapel
- (Clare) O’Callaghansmills
- (County Cork) Oysterhaven