21 cities
| City | County | 2026 Pop. ↓ |
|---|---|---|
| Olympia | Thurston County | 56,602 |
| Orchards | Clark County | 32,061 |
| Oak Harbor | Island County | 23,930 |
| Othello | Adams County | 9,222 |
| Orting | Pierce County | 8,840 |
| Ocean Shores | Grays Harbor County | 8,209 |
| Omak | Okanogan County | 5,319 |
| Otis Orchards-East Farms | Spokane County | 5,317 |
| Okanogan | Okanogan County | 2,548 |
| Oroville | Okanogan County | 1,960 |
| Ocean Park | Pacific County | 1,824 |
| Odessa | Lincoln County | 936 |
| Oakville | Grays Harbor County | 742 |
| Onalaska | Lewis County | 665 |
| Outlook | Yakima County | 553 |
| Oso | Snohomish County | 451 |
| Oakesdale | Whitman County | 379 |
| Ocosta | Grays Harbor County | 206 |
| Ocean City | Grays Harbor County | 90 |
| Oyehut | Grays Harbor County | 79 |
| Orient | Ferry County | 58 |