| County | Rank | Change (2020) ↓ | 2025 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Wahkiakum County | 1 | 10.59% | 4,919 | 4,448 |
| Lincoln County | 2 | 9.7% | 11,988 | 10,928 |
| Pend Oreille County | 3 | 9.67% | 14,807 | 13,502 |
| Skamania County | 4 | 8.05% | 13,010 | 12,041 |
| Stevens County | 5 | 7.2% | 49,945 | 46,591 |
| Douglas County | 6 | 6.78% | 45,948 | 43,029 |
| Lewis County | 7 | 6.29% | 87,748 | 82,553 |
| Benton County | 8 | 6.07% | 219,999 | 207,419 |
| Klickitat County | 9 | 5.9% | 24,161 | 22,814 |
| Grant County | 10 | 5.46% | 104,874 | 99,441 |
| Ferry County | 11 | 4.96% | 7,555 | 7,198 |
| Okanogan County | 12 | 4.93% | 44,216 | 42,139 |
| Clark County | 13 | 4.88% | 529,976 | 505,338 |
| Mason County | 14 | 4.23% | 68,825 | 66,034 |
| Columbia County | 15 | 4% | 4,107 | 3,949 |
| Pacific County | 16 | 3.89% | 24,410 | 23,495 |
| Kittitas County | 17 | 3.77% | 46,280 | 44,599 |
| Garfield County | 18 | 3.53% | 2,375 | 2,294 |
| Whatcom County | 19 | 3.13% | 234,561 | 227,449 |
| Cowlitz County | 20 | 3.11% | 114,464 | 111,014 |
| San Juan County | 21 | 2.96% | 18,354 | 17,826 |
| Franklin County | 22 | 2.87% | 99,938 | 97,150 |
| Jefferson County | 23 | 2.85% | 34,002 | 33,061 |
| Snohomish County | 24 | 2.83% | 853,379 | 829,933 |
| Grays Harbor County | 25 | 2.55% | 77,788 | 75,855 |
| Spokane County | 26 | 2.53% | 554,885 | 541,175 |
| Whitman County | 27 | 2.24% | 48,878 | 47,807 |
| Skagit County | 28 | 1.31% | 131,607 | 129,902 |
| Thurston County | 29 | 1.26% | 299,731 | 295,998 |
| Asotin County | 30 | 1.12% | 22,575 | 22,324 |
| Pierce County | 31 | 1.03% | 933,130 | 923,589 |
| Chelan County | 32 | 0.85% | 79,915 | 79,238 |
| Kitsap County | 33 | 0.55% | 277,348 | 275,823 |
| King County | 34 | 0.41% | 2,283,518 | 2,274,282 |
| Adams County | 35 | 0.28% | 20,664 | 20,607 |
| Clallam County | 36 | 0.15% | 77,480 | 77,367 |
| Yakima County | 37 | -0.33% | 255,891 | 256,733 |
| Island County | 38 | -1.79% | 85,437 | 86,998 |
| Walla Walla County | 39 | -2.59% | 60,998 | 62,623 |
Washington's counties show varied growth patterns from 2020 to 2025. Wahkiakum County leads with 10.59% annualized growth, followed by Lincoln County (9.7%) and Pend Oreille County (9.67%). The largest counties are King County (2,283,518), Pierce County (933,130), and Snohomish County (853,379). Of the 39 counties in Washington, 36 are growing while just 3 have experienced population decline. Overall, counties averaged 3.52% annualized growth, with total population growing by 1.88% annually.