| County | Rank | Change (2020) ↓ | 2025 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Lincoln County | 1 | 9.49% | 11,964 | 10,927 |
| Okanogan County | 2 | 8.87% | 45,886 | 42,147 |
| Wahkiakum County | 3 | 8.66% | 4,833 | 4,448 |
| Douglas County | 4 | 8.25% | 46,580 | 43,032 |
| Klickitat County | 5 | 7.62% | 24,560 | 22,820 |
| Grant County | 6 | 6.94% | 106,346 | 99,445 |
| Mason County | 7 | 6.78% | 70,510 | 66,033 |
| Garfield County | 8 | 6.57% | 2,448 | 2,297 |
| Benton County | 9 | 6.51% | 220,935 | 207,426 |
| Lewis County | 10 | 6.39% | 87,834 | 82,562 |
| Franklin County | 11 | 5.94% | 102,922 | 97,152 |
| Pend Oreille County | 12 | 5.89% | 14,302 | 13,506 |
| Ferry County | 13 | 5.79% | 7,614 | 7,197 |
| Snohomish County | 14 | 5.78% | 877,929 | 829,975 |
| Stevens County | 15 | 5.59% | 49,192 | 46,589 |
| Clark County | 16 | 5.28% | 532,071 | 505,363 |
| Skamania County | 17 | 5.28% | 12,681 | 12,045 |
| San Juan County | 18 | 5.08% | 18,731 | 17,826 |
| King County | 19 | 4.8% | 2,383,609 | 2,274,349 |
| Whatcom County | 20 | 4.3% | 237,222 | 227,451 |
| Kittitas County | 21 | 3.58% | 48,499 | 46,823 |
| Cowlitz County | 22 | 3.52% | 114,924 | 111,021 |
| Pacific County | 23 | 3.51% | 24,317 | 23,492 |
| Thurston County | 24 | 3.48% | 306,305 | 296,018 |
| Chelan County | 25 | 3.42% | 82,017 | 79,307 |
| Kitsap County | 26 | 3.39% | 285,190 | 275,832 |
| Jefferson County | 27 | 3.33% | 34,163 | 33,061 |
| Spokane County | 28 | 3.31% | 559,136 | 541,198 |
| Grays Harbor County | 29 | 3.1% | 78,216 | 75,863 |
| Adams County | 30 | 2.97% | 21,221 | 20,609 |
| Skagit County | 31 | 2.94% | 133,718 | 129,901 |
| Pierce County | 32 | 2.92% | 950,622 | 923,655 |
| Whitman County | 33 | 2.25% | 48,898 | 47,821 |
| Clallam County | 34 | 1.24% | 78,327 | 77,365 |
| Yakima County | 35 | 1.21% | 259,853 | 256,736 |
| Columbia County | 36 | 1.06% | 3,995 | 3,953 |
| Asotin County | 37 | 0.93% | 22,536 | 22,328 |
| Walla Walla County | 38 | -0.45% | 62,347 | 62,629 |
| Island County | 39 | -0.48% | 86,587 | 87,007 |
Washington's counties show varied growth patterns from 2020 to 2025. Lincoln County leads with 9.49% annualized growth, followed by Okanogan County (8.87%) and Wahkiakum County (8.66%). The largest counties are King County (2,383,609), Pierce County (950,622), and Snohomish County (877,929). Of the 39 counties in Washington, 37 are growing while just 2 have experienced population decline. Overall, counties averaged 4.49% annualized growth, with total population growing by 4.29% annually.
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