- Orléans
- Osgoode
- Ottawa East
- Ottawa South
- Overbrook
- Owen Sound
- Oliver
- Oriel
- Ostrander
- Oxford Centre
- Ojibway Island
- Oranmore
- Orrville
- Otter Lake
- Oak Lake
- Owenbrook
- O'Reilly's Bridge
- Ostryhon Corners
- Orr's Lake
- O'Grady Settlement
- Oakgrove
- Ogden's Beach
- Old Fort
- Orkney Beach
- Oro
- Oro Beach
- Oro Station
- Orr Lake
- O'Connor
- Ouimet