- Ocean
- O'Neill Island
- Oak Court
- Oak Grove
- Oak Hollow
- Oak Landing
- Oak Ridge Manor
- Oakbluff
- Oakdale
- Oakhill
- Oakland
- Oakland Hill
- Oakleigh Forest
- Oakmont
- Oaks of Severna Park
- Oakwood
- Oakwood Manor
- Oakwood Park
- Odenton Heights
- Odenton Park
- Old Annapolis Neck
- Old Cedar Point
- Old Colony Cove
- Old County Estates
- Old Glory Beach
- Old Mill
- Old Mill Bottom Estates
- Old Severna Park
- Orchard Gate at Piney Orchard
- Orchard Point at Piney Orchard