(Links below lead to Quick Facts for Idaho 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 |
| Idaho | 1,523,816 | 1,496,145 | 1,461,183 | 1,424,127 | 1,390,329 | 1,363,010 | 1,341,408 | 1,320,732 | 1,299,474 | 1,293,953 |
|---|---|---|---|---|---|---|---|---|---|---|
| Ada County | 380,920 | 373,158 | 360,869 | 346,749 | 333,322 | 326,196 | 320,867 | 313,472 | 303,139 | 300,904 |
| Adams County | 3,499 | 3,523 | 3,457 | 3,515 | 3,458 | 3,445 | 3,438 | 3,428 | 3,458 | 3,476 |
| Bannock County | 80,812 | 79,923 | 79,387 | 78,591 | 78,180 | 77,318 | 77,201 | 76,698 | 75,676 | 75,565 |
| Bear Lake County | 5,798 | 5,846 | 5,901 | 5,942 | 6,063 | 6,137 | 6,168 | 6,367 | 6,425 | 6,411 |
| Benewah County | 9,352 | 9,224 | 9,196 | 9,049 | 8,906 | 8,898 | 8,921 | 8,974 | 9,193 | 9,171 |
| Bingham County | 43,903 | 43,359 | 43,029 | 42,835 | 42,447 | 42,361 | 41,994 | 42,019 | 41,744 | 41,735 |
| Blaine County | 21,731 | 21,445 | 21,323 | 21,069 | 20,960 | 20,666 | 20,272 | 19,798 | 19,117 | 18,991 |
| Boise County | 7,504 | 7,542 | 7,441 | 7,225 | 7,215 | 7,151 | 6,988 | 6,822 | 6,747 | 6,670 |
| Bonner County | 41,168 | 40,996 | 40,350 | 39,891 | 39,094 | 38,577 | 37,789 | 37,083 | 36,998 | 36,835 |
| Bonneville County | 99,135 | 96,356 | 93,421 | 90,693 | 88,716 | 86,210 | 84,637 | 83,651 | 82,858 | 82,522 |
| Boundary County | 10,962 | 10,846 | 10,597 | 10,376 | 10,227 | 10,010 | 9,871 | 9,833 | 9,908 | 9,871 |
| Butte County | 2,751 | 2,756 | 2,732 | 2,780 | 2,780 | 2,820 | 2,898 | 2,852 | 2,899 | 2,899 |
| Camas County | 1,126 | 1,096 | 1,063 | 1,057 | 1,016 | 1,027 | 1,027 | 1,006 | 978 | 991 |
| Canyon County | 183,939 | 178,682 | 171,116 | 163,239 | 156,605 | 150,995 | 144,949 | 139,050 | 133,052 | 131,441 |
| Caribou County | 6,826 | 6,839 | 6,820 | 6,943 | 7,098 | 7,103 | 7,168 | 7,342 | 7,302 | 7,304 |
| Cassia County | 21,348 | 20,915 | 20,725 | 20,883 | 20,937 | 21,171 | 21,320 | 21,467 | 21,391 | 21,416 |
| Clark County | 910 | 895 | 899 | 883 | 894 | 874 | 942 | 962 | 1,024 | 1,022 |
| Clearwater County | 8,176 | 8,217 | 8,256 | 8,245 | 8,268 | 8,333 | 8,392 | 8,575 | 8,887 | 8,930 |
| Custer County | 4,254 | 4,156 | 4,090 | 4,020 | 4,081 | 4,083 | 4,124 | 4,214 | 4,336 | 4,342 |
| Elmore County | 28,997 | 28,864 | 28,320 | 28,590 | 29,064 | 28,881 | 29,306 | 29,189 | 29,092 | 29,130 |
| Franklin County | 12,454 | 12,158 | 12,003 | 12,009 | 11,906 | 11,677 | 11,662 | 11,452 | 11,351 | 11,329 |
| Fremont County | 12,551 | 12,501 | 12,382 | 12,270 | 12,367 | 12,171 | 11,909 | 11,841 | 11,784 | 11,819 |
| Gem County | 16,513 | 16,455 | 16,265 | 16,010 | 15,696 | 15,524 | 15,379 | 15,335 | 15,208 | 15,181 |
| Gooding County | 14,295 | 14,170 | 14,104 | 14,117 | 14,176 | 14,199 | 14,168 | 14,133 | 14,201 | 14,155 |
| Idaho County | 15,448 | 15,315 | 15,235 | 15,171 | 15,269 | 15,191 | 15,342 | 15,367 | 15,449 | 15,511 |
| Jefferson County | 23,860 | 22,777 | 21,844 | 21,222 | 20,501 | 20,006 | 19,663 | 19,265 | 19,212 | 19,155 |
| Jerome County | 20,468 | 19,986 | 19,603 | 19,200 | 18,966 | 18,683 | 18,533 | 18,448 | 18,427 | 18,342 |
| Kootenai County | 137,475 | 134,211 | 130,530 | 126,742 | 121,621 | 116,952 | 114,025 | 111,719 | 109,543 | 108,685 |
| Latah County | 35,906 | 35,748 | 36,077 | 35,950 | 35,835 | 35,460 | 35,173 | 35,318 | 34,886 | 34,935 |
| Lemhi County | 7,808 | 7,692 | 7,731 | 7,706 | 7,662 | 7,602 | 7,599 | 7,603 | 7,735 | 7,806 |
| Lewis County | 3,594 | 3,565 | 3,613 | 3,598 | 3,617 | 3,631 | 3,649 | 3,588 | 3,741 | 3,747 |
| Lincoln County | 4,503 | 4,473 | 4,376 | 4,394 | 4,224 | 4,215 | 4,150 | 4,114 | 4,047 | 4,044 |
| Madison County | 37,456 | 36,974 | 36,496 | 35,106 | 33,545 | 31,057 | 29,632 | 28,108 | 27,465 | 27,467 |
| Minidoka County | 18,645 | 18,509 | 18,491 | 18,536 | 18,796 | 19,103 | 19,357 | 19,506 | 20,087 | 20,174 |
| Nez Perce County | 38,975 | 38,820 | 38,494 | 38,051 | 37,792 | 37,692 | 37,124 | 37,006 | 37,399 | 37,410 |
| Oneida County | 4,130 | 4,092 | 4,081 | 4,108 | 4,065 | 4,073 | 4,118 | 4,171 | 4,136 | 4,125 |
| Owyhee County | 10,877 | 10,763 | 10,695 | 10,695 | 10,759 | 10,863 | 10,780 | 10,822 | 10,684 | 10,644 |
| Payette County | 22,966 | 22,689 | 22,091 | 21,675 | 21,295 | 21,255 | 21,062 | 20,849 | 20,634 | 20,578 |
| Power County | 7,683 | 7,648 | 7,656 | 7,553 | 7,575 | 7,402 | 7,462 | 7,482 | 7,500 | 7,538 |
| Shoshone County | 12,913 | 12,808 | 12,890 | 12,801 | 12,693 | 12,819 | 12,990 | 13,413 | 13,726 | 13,771 |
| Teton County | 8,833 | 8,294 | 7,758 | 7,396 | 7,147 | 6,970 | 6,721 | 6,399 | 6,104 | 5,999 |
| Twin Falls County | 74,284 | 72,841 | 71,053 | 69,151 | 67,788 | 66,696 | 65,232 | 64,423 | 64,325 | 64,284 |
| Valley County | 8,862 | 8,925 | 8,665 | 8,127 | 7,783 | 7,632 | 7,519 | 7,640 | 7,638 | 7,651 |
| Washington County | 10,206 | 10,093 | 10,058 | 9,964 | 9,920 | 9,881 | 9,887 | 9,928 | 9,968 | 9,977 |
Source: Population Division, U.S. Census Bureau