- O'Connor
- O'Grady Settlement
- O'Reilly's Bridge
- Oak Flats
- Oak Heights
- Oak Lake
- Oak Leaf
- Oakdale
- Oakgrove
- Oakland
- Oakville
- Oconto
- Odessa
- Ogden's Beach
- Oil Springs
- Ojibway Island
- Old Fort
- Old Spring Bay
- Old Stittsville
- Old Woman's River
- Oliver
- Olivet
- Omemee
- Ompah
- Opasatika
- Orangeville
- Oranmore
- Orchard Beach
- Orchardville
- Oriel