Barrios de California O
- Oak Creek
- Oak Grove
- Oak Grove Manor
- Oak Knoll
- Oak Knoll Golf Links
- Oak Knoll-Redwood Park
- Oak Park
- Oak Park
- Oak Park
- Oak View
- Ocean Beach
- Ocean Crest
- Ocean Hills
- Ocean Park
- Oceana
- Ohlone
- Oildale
- Old Agoura
- Old Davis North
- Old East Davis
- Old Las Palmas
- Old Mill
- Old Monterey
- Old North Sacramento
- Old Oakland
- Old Palo Alto
- Old Sacramento
- Old San Leandro
- Old Town
- Old Town
- Old Town Kern
- Old Town Pasadena
- Old Towne Orange
- Olde Torrance Neighborhood
- Oleander/Sunset
- Olinder
- Olive Drive
- Olive Drive Area
- Olive Heights
- Olivenhain
- Olympia
- Olympus Pointe
- Orange Park
- Orchard Hills
- Orchard Park
- Ord Grove
- Ortega Park
- Otay Mesa
- Otay Mesa West
- Otay Ranch
- Otay Ranch Village
- Otay Town
- Outer Mission
- Outer Monterey
- Outer Seaport
- Outer Sunset
- Overfelt
- Oxnard Shores