21 cities
| City | County | 2025 Pop. ↓ |
|---|---|---|
| Olympia | Thurston County | 56,436 |
| Orchards | Clark County | 31,628 |
| Oak Harbor | Island County | 24,046 |
| Othello | Adams County | 9,111 |
| Orting | Pierce County | 8,875 |
| Ocean Shores | Grays Harbor County | 7,970 |
| Otis Orchards-East Farms | Spokane County | 5,569 |
| Omak | Okanogan County | 5,243 |
| Okanogan | Okanogan County | 2,518 |
| Ocean Park | Pacific County | 1,989 |
| Oroville | Okanogan County | 1,935 |
| Odessa | Lincoln County | 930 |
| Oakville | Grays Harbor County | 738 |
| Onalaska | Lewis County | 593 |
| Oakesdale | Whitman County | 381 |
| 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 |