- Ogema
- Oil City
- Ojibwa
- Okauchee
- Okauchee Lake
- Okee
- Old Albertville
- Old Ashippun
- Old Deerfield
- Old Fort
- Old Lebanon
- Old Scribbler Island
- Oliver
- Olivet
- Olmstead Island
- Olympic Village
- Omro
- Onalaska
- Onaway Island
- Ondaig Island
- Oneida
- Onemile Island
- Ono
- Ontario
- Oostburg
- Orange Mill
- Orchard Grove
- Oregon
- Orfordville
- Orihula