13 cities
| City | County | 2026 Pop. ↓ |
|---|---|---|
| Oregon City | Clackamas County | 38,603 |
| Oak Grove | Clackamas County | 17,588 |
| Oatfield | Clackamas County | 12,546 |
| Ontario | Malheur County | 12,052 |
| Oak Hills | Washington County | 11,494 |
| Oakridge | Lane County | 3,132 |
| Odell | Hood River County | 2,761 |
| Oakland | Douglas County | 954 |
| Oregon Shores | Klamath County | 767 |
| Orient | Clackamas County | 535 |
| O'Brien | Josephine County | 534 |
| Oceanside | Tillamook County | 437 |
| Ochoco West | Crook County | 418 |