City | 2024 Population |
|---|---|
| Oak Glen | 431 |
| Oak Hills | 5,268 |
| Oak Park | 13,759 |
| Oak Run | 743 |
| Oak Shores | 57 |
| Oak View | 6,379 |
| Oakdale | 22,988 |
| Oakhurst | 4,601 |
| Oakland | 435,024 |
| Oakley | 46,521 |
| Oasis | 4,996 |
| Occidental | 931 |
| Oceano | 7,119 |
| Oceanside | 168,705 |
| Ocotillo | 104 |
| Oildale | 34,072 |
| Ojai | 7,410 |
| Olancha | 161 |
| Old Fig Garden | 4,699 |
| Old River | 136 |
| Old Stine | 3,747 |
| Olde Stockdale | 247 |
| Olivehurst | 19,683 |
| Ontario | 184,705 |
| Onyx | 613 |
| Orange | 137,965 |
| Orange Blossom | 1,885 |
| Orange Cove | 9,447 |
| Orangevale | 36,098 |
| Orcutt | 30,921 |
| Orick | 324 |
| Orinda | 19,314 |
| Orland | 8,067 |
| Orosi | 9,292 |
| Oroville | 19,267 |
| Oroville East | 7,518 |
| Oxnard | 197,347 |