O
- (Laois) Old Town
- (Wexford) Old Ross
- (County Carlow) Oldleighlin
- (Wicklow) Oldcourt
- (Wexford) Oldcourt
- (Wicklow) Oldbridge
- (Wexford) Orristown Cross Roads
- (Wexford) Oulartwick
- (County Carlow) Orchard Bridge
- (Wexford) Old Town
- (Wexford) Oldcourt
- (Laois) Oldleagh
- (Kilkenny) Ossoryhill
- (Kilkenny) Oldgrange
- (Kilkenny) Oldtown
- (Kilkenny) Oldcourt
- (Wexford) Oulart
- (Wexford) Oilgate
- (Fingal County) Oldtown
- (Louth) Omeath
- (Kildare) Oughterard
- (Meath) Oldcastle
- (Kildare) Old Kilcullen
- (South Dublin) Oldbawn