- Old Bayside
- Old Hickory
- Old House Cove Estates
- Olde Mill
- Oldfield
- Olivet
- Owen Soper Woods
- Owensville
- Owings Farm
- Owings Hills
- Owings Station
- Owings Town Center
- Owings Wood
- Oak Grove
- Oakridge
- Oakwood
- Octararo Lakes
- Octoraro
- Octoraro Park
- Oddessy
- Old Field Point
- Old Line Village of Fair Hill
- Oldfield Acres
- Orchard View
- Oakland Acres
- Oil City
- Oakdale Manor
- Oakland
- Oakland Hills
- Oakleigh Ridge