- Oak Island
- Old Fort
- Otter Island
- Outer Island
- Oulu
- Olympic Village
- Oakland
- Old Albertville
- Okee
- Otsego
- Oak Hall
- Oak Knoll
- Oak Park Terrace
- Oakland Heights
- Old Deerfield
- Oak Grove
- Old Ashippun
- Old Lebanon
- Onemile Island
- Ondaig Island
- Oak Ridge Village Mobile Home Park
- Oak Center
- Oakley
- Otter Island
- Orva
- Oregon
- Osseo
- Owen
- Oakdale
- Oakfield