- Oak Lawn Mobile Home Park
- Ottville
- Old Princeton
- Old Stonington
- Osbernville
- Oak Point
- Oakcrest
- Oilfield
- Orange
- Oskaloosa
- Old State Mobile Home Village
- Oak Park Township
- Oakglen
- Oakton
- Oasis Mobile Home Park
- Old Colony Court
- Oliver Lane Subdivision
- Olson's Subdivision
- Orchard Subdivision
- Oury Point
- Oil Center
- Oil Grove
- Ospur
- Ontarioville
- Oak Grove
- Oakdale
- Oakland
- Oakwood
- Ogden
- Omaha