- Ogdensburg
- Oliver
- Oneida
- Ontario
- Osceola
- Oxford
- Oak Hill
- Oakland
- Orange Mill
- Oakwood Mobile Home Community
- Ormsby
- Otis
- Osman
- Oakwood
- Oil City
- Oak Orchard
- Olmstead Island
- Oak Hill Mobile Home Park
- Oakridge
- Olivet
- Ono
- Ottman Corners
- Oakdale Estates
- Orion
- Oak Creek
- Oconomowoc
- Oconomowoc Lake
- Oconto
- Oconto Falls
- Odanah