- Odell
- Oldham
- Opperman
- O'Bryonsville
- Oakdale
- Oakley
- Oakley Square
- Over-The-Rhine
- Oak Avenue Mobile Home Park
- Olde Town Mobile Home Park
- Otterbein
- Oak Manor
- Oak Park
- Oak Ridge
- Oval City
- Oak Leaf Mobile Home Park
- Oak Mobile Home Court
- Oregon Corners
- Osborn Corners
- Oak Forest
- Oak Hill Mobile Home Park
- Oakfield
- Old Town
- Otter
- Old Gore
- Orbiston
- Oreton
- Oreville
- Orland
- Osceola