| County | Rank | Change (2020) ↓ | 2026 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Lincoln County | 1 | 11.08% | 12,137 | 10,926 |
| Wahkiakum County | 2 | 10.95% | 4,933 | 4,446 |
| Douglas County | 3 | 10.22% | 47,429 | 43,033 |
| Mason County | 4 | 9.89% | 72,571 | 66,041 |
| Okanogan County | 5 | 8.71% | 45,812 | 42,143 |
| Benton County | 6 | 8.25% | 224,513 | 207,408 |
| Klickitat County | 7 | 8.06% | 24,657 | 22,817 |
| Lewis County | 8 | 7.8% | 88,993 | 82,551 |
| Pend Oreille County | 9 | 7.72% | 14,547 | 13,505 |
| Stevens County | 10 | 7.67% | 50,158 | 46,585 |
| Grant County | 11 | 7.21% | 106,620 | 99,446 |
| Columbia County | 12 | 7.13% | 4,236 | 3,954 |
| Franklin County | 13 | 6.9% | 103,838 | 97,137 |
| Clark County | 14 | 6.47% | 537,997 | 505,325 |
| Snohomish County | 15 | 6.07% | 880,242 | 829,901 |
| Garfield County | 16 | 5.88% | 2,431 | 2,296 |
| Kittitas County | 17 | 5.72% | 49,499 | 46,823 |
| Skamania County | 18 | 5.45% | 12,694 | 12,038 |
| Adams County | 19 | 5.07% | 21,654 | 20,610 |
| Whatcom County | 20 | 4.72% | 238,183 | 227,452 |
| Cowlitz County | 21 | 4.5% | 116,006 | 111,014 |
| San Juan County | 22 | 4.34% | 18,598 | 17,825 |
| King County | 23 | 4.29% | 2,371,919 | 2,274,304 |
| Pacific County | 24 | 4.14% | 24,477 | 23,503 |
| Chelan County | 25 | 4.03% | 82,500 | 79,302 |
| Ferry County | 26 | 4% | 7,487 | 7,199 |
| Spokane County | 27 | 3.71% | 561,203 | 541,144 |
| Kitsap County | 28 | 3.7% | 286,020 | 275,811 |
| Thurston County | 29 | 3.51% | 306,390 | 296,013 |
| Grays Harbor County | 30 | 3.17% | 78,268 | 75,866 |
| Pierce County | 31 | 3.16% | 952,790 | 923,609 |
| Jefferson County | 32 | 2.98% | 34,049 | 33,064 |
| Skagit County | 33 | 2.94% | 133,700 | 129,885 |
| Whitman County | 34 | 2.81% | 49,161 | 47,816 |
| Clallam County | 35 | 1.45% | 78,474 | 77,356 |
| Yakima County | 36 | 1.05% | 259,399 | 256,716 |
| Asotin County | 37 | 1.01% | 22,552 | 22,327 |
| Walla Walla County | 38 | -0.01% | 62,613 | 62,620 |
| Island County | 39 | -1.92% | 85,332 | 87,001 |
Washington's counties show varied growth patterns from 2020 to 2026. Lincoln County leads with 1.77% annualized growth, followed by Wahkiakum County (1.75%) and Douglas County (1.63%). The largest counties are King County (2,371,919), Pierce County (952,790), and Snohomish County (880,242). Of the 39 counties in Washington, 37 are growing while just 2 have experienced population decline. Overall, counties averaged 0.85% annualized growth, with total population growing by 0.74% annually.
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