- Oak Grove
- O'Hara Township
- Oak Hill
- Oakland
- Option
- Orville
- Otto
- Overbrook
- Oak Ridge
- Old Gum Tree
- Olivet
- Oscar
- Ohioview
- Old Furnace
- Oppenheimer
- Ott Town
- Orwell
- Overshot
- Overton
- Owl Hollow
- Oakbrook
- Oakbrook Terrace
- Oley Furnace
- Oley Line
- Ontelaunee
- Ontelaunee Heights
- Orchard Hills
- Oreville
- Overbrook
- Overlook Woods