- Oakwood
- Otsego Center
- Oakford
- Oakville
- Odell
- Ora
- Otisco
- Otwell
- Owensburg
- Octagon
- Old Halfway
- Otter Creek Junction
- Old Town
- Olin
- Old Pekin
- Organ Springs
- Oakdale
- Old Bargersville
- Orrville
- Ormas
- Oakwood Park
- Ogden Island
- Osborn Landing
- Oswego
- Oak Lodge
- Ontario
- Oakwood Mobile Home Park
- Orchard Grove
- Osborn
- Oakwood