- Orchards of Linthicum
- Orr Acres
- Osborne Heights
- Owings Beach
- Oyster Harbor
- Oak Island (historical)
- Oak Forest
- Oak Forest Park
- Oak Hill
- Oak Park
- Oak Summit
- Oak Valley
- Oakdale
- Oakhurst
- Oakland
- Oakland Park
- Oakleigh
- Oakleigh Manor
- Oaks of Parsonage
- Oakwood Village
- Oella
- Offutt Ridge
- Old York Manor
- Olde Mill Estates
- Oliver Beach
- Orchard Hills
- Oregon
- Overlook
- Owings Ridge
- Odyssey