- Oklee
- Okorb Island
- Old Frontenac
- Old Mesaba
- Olga
- Oliver Island
- Olivia
- Olson's Mobile Home Park
- Olson's Mobile Home Park
- Olson's Mobile Park
- Onamia
- One Tree Island
- Onega
- Oneota
- Onigum
- Onstad Trailer Park
- Opole
- Opstead
- Orchard Garden
- Oreland
- Org
- Orleans
- Ormonds Island
- Ormsby
- Orono
- Oronoco
- Oronoco Estates
- Orr
- Orrock
- Orth