- Oldleighlin
- Oldtown
- Orchard Bridge
- Old Connaught
- Oldtown
- O’Neill’s Cross Roads
- Oakfield
- Obelisks
- Oghill Bridge
- Oldcourt
- Oldgrange
- Oldtowndonore
- Oughterard
- Oldcourt
- Oldgrange
- Oldtown
- Oldtown
- Oldtown
- Ossoryhill
- Ovenstown
- Owning
- Old Town
- Oldleagh
- Omeath
- Oakstown
- Odder
- Oldcastle
- Oldtown
- Oldtown
- Ongenstown