O
- (Kildare) Oakfield
- (Wexford) Old Bawn
- (Wexford) Oldtown Cross Roads
- (Wicklow) Oghil
- (Kilkenny) Owning
- (Kilkenny) Ovenstown
- (Kilkenny) Oldtown
- (Kilkenny) Oldtown
- (Kildare) Oldcourt
- (Kildare) Oldgrange
- (Kildare) Obelisks
- (Kildare) Oghill Bridge
- (Kildare) O’Neill’s Cross Roads
- (Wicklow) Oghi Upper
- (Kildare) Oldtowndonore
- (Wicklow) Oldboleys
- (Dún Laoghaire-Rathdown) Old Connaught
- (Wexford) Our Lady's Island
- (Westmeath) Oldtown
- (Meath) Odder
- (Meath) Oldtown
- (Meath) Ongenstown
- (Meath) Oakstown
- (Meath) Otterstown
- (Meath) Oldtown
- (Wexford) Oulartleigh
- (Wicklow) Oghil Lower
- (County Carlow) Oldtown
- (Uíbh Fhailí) Oughter
- (Meath) Oristown