- O’Brien’s Bridge
- O’Briensbridge
- O’Callaghansmills
- Oatfield
- Ogonnelloe
- Oil Mill Bridge
- Oldtown
- Oughtdarra
- Oughterard
- Oughtmama
- O'Callagha Park
- Old Bride Bridge
- Old Chapel Cross Roads
- Old Courth
- Old Port House
- Old Twopothouse Cross Roads
- Oldcastletown
- Oldchapel
- Oldcourt
- Orthon Island
- Ovens
- Owen’s Island
- Oysterhaven
- Oakhampton
- Oaklands
- Oldgrange
- Orkneys Cross Roads
- Outeragh
- Old Pike Bridge
- O’Connell Bridge