21 cities
| City | County | 2025 Pop. ↓ |
|---|---|---|
| Olympia | Thurston County | 55,816 |
| Orchards | Clark County | 31,628 |
| Oak Harbor | Island County | 23,610 |
| Othello | Adams County | 9,093 |
| Orting | Pierce County | 8,892 |
| Ocean Shores | Grays Harbor County | 8,067 |
| Otis Orchards-East Farms | Spokane County | 5,569 |
| Omak | Okanogan County | 5,099 |
| Okanogan | Okanogan County | 2,450 |
| Ocean Park | Pacific County | 1,989 |
| Oroville | Okanogan County | 1,880 |
| Odessa | Lincoln County | 946 |
| Oakville | Grays Harbor County | 732 |
| Onalaska | Lewis County | 593 |
| Oakesdale | Whitman County | 392 |
| Outlook | Yakima County | 352 |
| Oso | Snohomish County | 346 |
| Ocosta | Grays Harbor County | 139 |
| Ocean City | Grays Harbor County | 84 |
| Oyehut | Grays Harbor County | 64 |
| Orient | Ferry County | 30 |