- Ojai
- Ojai Valley Estates Mobile Home Park
- Ojala
- Olancha
- Olcott
- Old Adobe
- Old Bailey Place
- Old Bretz Mill
- Old Corral
- Old Dale
- Old Fig Garden
- Old Forbestown
- Old Fort Jim
- Old Garlock
- Old Gilroy
- Old Hilltown
- Old Hopland
- Old Hulbert Place
- Old Mammoth
- Old Mill Park Mobile Home Park
- Old Ornbaun Hot Springs
- Old Pino
- Old Point Comfort
- Old Red Rock Place
- Old River
- Old Station
- Old Town
- Old Town
- Oleander
- Olema