- Ocean View Village
- Oceanville
- Ogontz
- Ogren
- Ogunquit
- Ohio Island
- Olamon
- Olamon Island
- Olamon Island
- Old
- Old City
- Old Man
- Old Orchard Beach
- Old Soaker
- Old Town
- Old Town Landing
- Oldfields
- Oliver Hill Corner
- Onawa
- Opechee Island
- Oquossoc
- Orffs Corner
- Orient
- Orland
- Orono
- Orono Island
- Orono Island
- Orrington
- Orrington Center
- Orrs Island