- Oak Mills
- Oak Ridge Mobile Home Community
- Osro
- Oak Hill
- Oakley
- Ogden
- Olivet
- Oneida
- Oswego
- Otis
- Ottawa
- Oxford
- Oberlin
- Olpe
- Osborne
- Oskaloosa
- Ottawa Junction
- Obeeville
- Oak Valley
- Odin
- Ogallah
- Opolis
- Ottumwa
- Oaks Mobile Home Park
- Oak Court Mobile Home Court
- Oaklawn
- Oakwood Manor Mobile Home Park
- Oatville
- Orchard Park Mobile Home Park
- Oakland