- Oswego Center
- Otto Mills
- Oaksville
- Oneida Village Mobile Home Park
- Otsdawa
- Otsego
- Oscawana Corners
- Oakland Gardens
- Old Germania Heights
- Oakwood
- Oakwood Beach
- Oakwood Heights Station
- Old Place
- Old Town Station
- Oakbrook
- Oak Island
- Oak Point
- Oakvale
- Ogden Island
- Old Man Island
- Oliver Island
- Owatonna Island
- Oakwood Terrace
- Orchard Park
- Overlook
- Old Central Bridge
- Owlsville
- Osgood Landing
- Old Field Mobile Home Park
- Oak Island