(Links below lead to Quick Facts for Washington Counties: People, Business & Geography at U.S. Census Bureau.)
| Area | 7/1/2008 | 7/1/2007 | 7/1/2006 | 7/1/2005 | 7/1/2004 | 7/1/2003 | 7/1/2002 | 7/1/2001 | 7/1/2000 | Census 2000 |
| Washington | 6,549,224 | 6,449,511 | 6,360,529 | 6,254,579 | 6,179,645 | 6,110,202 | 6,055,613 | 5,987,181 | 5,911,104 | 5,894,121 |
|---|---|---|---|---|---|---|---|---|---|---|
| Adams County | 17,285 | 16,887 | 16,559 | 16,516 | 16,350 | 16,370 | 16,286 | 16,173 | 16,443 | 16,428 |
| Asotin County | 21,420 | 21,085 | 21,051 | 20,910 | 20,798 | 20,507 | 20,517 | 20,470 | 20,555 | 20,551 |
| Benton County | 163,058 | 158,781 | 157,049 | 155,930 | 154,276 | 152,513 | 149,671 | 145,574 | 143,085 | 142,475 |
| Chelan County | 71,540 | 70,694 | 69,825 | 68,892 | 68,021 | 67,277 | 66,856 | 66,656 | 66,678 | 66,616 |
| Clallam County | 71,021 | 70,317 | 69,579 | 68,701 | 67,409 | 66,325 | 65,811 | 64,791 | 64,286 | 64,525 |
| Clark County | 424,733 | 416,493 | 408,071 | 399,660 | 389,229 | 377,274 | 368,700 | 358,515 | 347,526 | 345,238 |
| Columbia County | 3,990 | 3,964 | 3,950 | 4,020 | 4,067 | 4,033 | 4,018 | 4,046 | 4,071 | 4,064 |
| Cowlitz County | 101,254 | 100,216 | 98,685 | 96,231 | 95,328 | 94,355 | 94,270 | 93,598 | 92,999 | 92,948 |
| Douglas County | 36,653 | 36,035 | 35,142 | 34,343 | 33,888 | 33,345 | 32,985 | 32,772 | 32,683 | 32,603 |
| Ferry County | 7,353 | 7,344 | 7,474 | 7,455 | 7,447 | 7,396 | 7,266 | 7,278 | 7,276 | 7,260 |
| Franklin County | 72,783 | 69,124 | 65,815 | 62,427 | 59,021 | 56,069 | 52,803 | 50,771 | 49,606 | 49,347 |
| Garfield County | 2,060 | 2,044 | 2,117 | 2,191 | 2,205 | 2,268 | 2,265 | 2,302 | 2,389 | 2,397 |
| Grant County | 84,697 | 82,361 | 80,845 | 79,531 | 78,767 | 78,002 | 77,046 | 76,141 | 74,966 | 74,698 |
| Grays Harbor County | 71,342 | 71,181 | 70,727 | 70,109 | 69,606 | 69,020 | 68,300 | 67,997 | 67,147 | 67,194 |
| Island County | 81,424 | 80,975 | 80,747 | 79,603 | 79,270 | 76,596 | 75,566 | 74,143 | 71,847 | 71,558 |
| Jefferson County | 29,542 | 29,159 | 29,001 | 28,401 | 27,860 | 27,519 | 27,166 | 26,827 | 26,419 | 25,953 |
| King County | 1,875,519 | 1,850,714 | 1,827,533 | 1,799,085 | 1,779,905 | 1,767,851 | 1,762,693 | 1,756,766 | 1,739,415 | 1,737,034 |
| Kitsap County | 239,769 | 238,160 | 239,771 | 236,024 | 239,179 | 238,884 | 236,623 | 233,304 | 232,340 | 231,969 |
| Kittitas County | 38,951 | 38,163 | 37,844 | 36,955 | 36,506 | 35,399 | 34,764 | 33,888 | 33,508 | 33,362 |
| Klickitat County | 20,377 | 20,054 | 19,780 | 19,401 | 19,341 | 19,329 | 19,139 | 19,211 | 19,214 | 19,161 |
| Lewis County | 74,132 | 73,513 | 72,662 | 71,597 | 70,673 | 70,112 | 69,334 | 68,891 | 68,616 | 68,600 |
| Lincoln County | 10,344 | 10,244 | 10,202 | 10,186 | 10,318 | 10,124 | 10,053 | 10,119 | 10,175 | 10,184 |
| Mason County | 57,846 | 56,859 | 55,268 | 53,822 | 52,727 | 51,535 | 50,689 | 49,989 | 49,551 | 49,405 |
| Okanogan County | 40,033 | 39,494 | 39,116 | 39,002 | 38,758 | 38,514 | 38,845 | 39,115 | 39,550 | 39,564 |
| Pacific County | 21,271 | 21,417 | 21,341 | 21,230 | 20,973 | 20,908 | 20,543 | 20,649 | 20,932 | 20,984 |
| Pend Oreille County | 12,859 | 12,726 | 12,633 | 12,343 | 12,248 | 12,049 | 11,973 | 11,863 | 11,738 | 11,732 |
| Pierce County | 785,639 | 773,105 | 763,687 | 749,202 | 741,242 | 736,193 | 728,443 | 716,210 | 703,968 | 700,820 |
| San Juan County | 15,294 | 15,182 | 15,116 | 15,073 | 15,006 | 14,745 | 14,619 | 14,345 | 14,147 | 14,077 |
| Skagit County | 118,000 | 115,898 | 114,136 | 111,963 | 110,076 | 108,205 | 106,126 | 104,828 | 103,466 | 102,979 |
| Skamania County | 10,794 | 10,698 | 10,507 | 10,284 | 10,225 | 10,039 | 9,888 | 9,832 | 9,893 | 9,872 |
| Snohomish County | 683,655 | 674,406 | 662,757 | 649,083 | 639,390 | 632,921 | 629,675 | 621,183 | 609,112 | 606,024 |
| Spokane County | 462,677 | 456,004 | 446,932 | 440,431 | 435,225 | 430,991 | 427,083 | 422,780 | 418,806 | 417,939 |
| Stevens County | 42,050 | 41,741 | 41,234 | 40,804 | 40,387 | 40,109 | 40,024 | 40,041 | 40,180 | 40,066 |
| Thurston County | 245,181 | 238,166 | 232,862 | 227,476 | 223,417 | 219,993 | 216,549 | 212,509 | 208,283 | 207,355 |
| Wahkiakum County | 4,133 | 4,038 | 3,941 | 3,830 | 3,737 | 3,664 | 3,792 | 3,780 | 3,837 | 3,824 |
| Walla Walla County | 57,788 | 57,129 | 56,923 | 56,933 | 56,963 | 56,364 | 55,866 | 55,198 | 55,224 | 55,180 |
| Whatcom County | 196,529 | 192,353 | 188,289 | 185,180 | 181,575 | 177,699 | 174,888 | 171,196 | 167,726 | 166,814 |
| Whitman County | 41,664 | 40,766 | 41,219 | 41,533 | 41,125 | 40,659 | 40,993 | 40,551 | 40,721 | 40,740 |
| Yakima County | 234,564 | 232,021 | 230,139 | 228,222 | 227,107 | 225,046 | 223,485 | 222,879 | 222,726 | 222,581 |
Source: Population Division, U.S. Census Bureau