| County | Rank | Change (2020) ↓ | 2026 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Okanogan County | 1 | 11.11% | 46,830 | 42,147 |
| Lincoln County | 2 | 10.42% | 12,066 | 10,927 |
| Douglas County | 3 | 10.07% | 47,365 | 43,032 |
| Klickitat County | 4 | 9.54% | 24,996 | 22,820 |
| Wahkiakum County | 5 | 9.4% | 4,866 | 4,448 |
| Grant County | 6 | 8.58% | 107,975 | 99,445 |
| Garfield County | 7 | 8.49% | 2,492 | 2,297 |
| Mason County | 8 | 8.11% | 71,388 | 66,033 |
| Benton County | 9 | 7.84% | 223,680 | 207,426 |
| Franklin County | 10 | 7.67% | 104,606 | 97,152 |
| Snohomish County | 11 | 7.44% | 891,745 | 829,975 |
| Lewis County | 12 | 7.34% | 88,619 | 82,562 |
| Ferry County | 13 | 6.78% | 7,685 | 7,197 |
| King County | 14 | 6.71% | 2,427,007 | 2,274,349 |
| Clark County | 15 | 6.24% | 536,873 | 505,363 |
| Stevens County | 16 | 5.97% | 49,369 | 46,589 |
| Pend Oreille County | 17 | 5.67% | 14,272 | 13,506 |
| Skamania County | 18 | 5.45% | 12,702 | 12,045 |
| San Juan County | 19 | 5.43% | 18,794 | 17,826 |
| Whatcom County | 20 | 5.29% | 239,490 | 227,451 |
| Kitsap County | 21 | 4.76% | 288,960 | 275,832 |
| Thurston County | 22 | 4.62% | 309,698 | 296,018 |
| Chelan County | 23 | 4.41% | 82,806 | 79,307 |
| Cowlitz County | 24 | 4.36% | 115,866 | 111,021 |
| Kittitas County | 25 | 4.28% | 48,826 | 46,823 |
| Jefferson County | 26 | 4% | 34,382 | 33,061 |
| Pierce County | 27 | 3.94% | 960,074 | 923,655 |
| Spokane County | 28 | 3.9% | 562,325 | 541,198 |
| Adams County | 29 | 3.85% | 21,403 | 20,609 |
| Pacific County | 30 | 3.82% | 24,389 | 23,492 |
| Skagit County | 31 | 3.69% | 134,700 | 129,901 |
| Grays Harbor County | 32 | 3.53% | 78,539 | 75,863 |
| Whitman County | 33 | 3.3% | 49,397 | 47,821 |
| Yakima County | 34 | 1.73% | 261,183 | 256,736 |
| Clallam County | 35 | 1.72% | 78,696 | 77,365 |
| Asotin County | 36 | 0.99% | 22,549 | 22,328 |
| Columbia County | 37 | 0.3% | 3,965 | 3,953 |
| Walla Walla County | 38 | 0% | 62,626 | 62,629 |
| Island County | 39 | -0.36% | 86,696 | 87,007 |
Washington's counties show varied growth patterns from 2020 to 2026. Okanogan County leads with 1.77% annualized growth, followed by Lincoln County (1.67%) and Douglas County (1.61%). The largest counties are King County (2,427,007), Pierce County (960,074), and Snohomish County (891,745). Of the 39 counties in Washington, 37 are growing while just 2 have experienced population decline. Overall, counties averaged 0.87% annualized growth, with total population growing by 0.91% annually.
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