| County | Rank | Change (2020) ↓ | 2026 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Boundary County | 1 | 21.62% | 14,766 | 12,141 |
| Canyon County | 2 | 21.53% | 283,192 | 233,031 |
| Bonner County | 3 | 19.06% | 56,447 | 47,411 |
| Gem County | 4 | 18.29% | 22,803 | 19,278 |
| Camas County | 5 | 17.8% | 1,277 | 1,084 |
| Adams County | 6 | 17.47% | 5,198 | 4,425 |
| Jefferson County | 7 | 15.96% | 36,044 | 31,082 |
| Teton County | 8 | 15.32% | 13,532 | 11,734 |
| Benewah County | 9 | 12.61% | 10,787 | 9,579 |
| Kootenai County | 10 | 12.56% | 194,495 | 172,791 |
| Lincoln County | 11 | 12.54% | 5,780 | 5,136 |
| Boise County | 12 | 12.53% | 8,623 | 7,663 |
| Jerome County | 13 | 11.34% | 27,020 | 24,268 |
| Franklin County | 14 | 11.2% | 15,882 | 14,283 |
| Ada County | 15 | 11.18% | 554,017 | 498,301 |
| Payette County | 16 | 11.06% | 28,418 | 25,588 |
| Custer County | 17 | 10.78% | 4,729 | 4,269 |
| Bonneville County | 18 | 10.62% | 137,982 | 124,736 |
| Valley County | 19 | 10.38% | 13,071 | 11,842 |
| Oneida County | 20 | 9.95% | 5,018 | 4,564 |
| Washington County | 21 | 9.86% | 11,601 | 10,560 |
| Fremont County | 22 | 9.4% | 14,681 | 13,419 |
| Twin Falls County | 23 | 9.23% | 98,719 | 90,374 |
| Latah County | 24 | 8.88% | 43,158 | 39,638 |
| Power County | 25 | 8.35% | 8,541 | 7,883 |
| Bingham County | 26 | 7.84% | 51,871 | 48,099 |
| Idaho County | 27 | 7.78% | 17,880 | 16,590 |
| Shoshone County | 28 | 6.61% | 14,078 | 13,205 |
| Madison County | 29 | 6.59% | 56,401 | 52,912 |
| Bear Lake County | 30 | 6.35% | 6,771 | 6,367 |
| Minidoka County | 31 | 6.23% | 23,021 | 21,671 |
| Cassia County | 32 | 6.22% | 26,294 | 24,755 |
| Owyhee County | 33 | 6.01% | 12,720 | 11,999 |
| Bannock County | 34 | 5.25% | 91,860 | 87,281 |
| Lewis County | 35 | 5.11% | 3,704 | 3,524 |
| Butte County | 36 | 4.96% | 2,711 | 2,583 |
| Blaine County | 37 | 4.43% | 25,423 | 24,345 |
| Gooding County | 38 | 4.37% | 16,341 | 15,657 |
| Lemhi County | 39 | 4.26% | 8,297 | 7,958 |
| Elmore County | 40 | 3.82% | 29,775 | 28,680 |
| Clearwater County | 41 | 3.62% | 9,069 | 8,752 |
| Caribou County | 42 | 3.35% | 7,251 | 7,016 |
| Nez Perce County | 43 | 1.04% | 42,585 | 42,148 |
| Clark County | 44 | -1.64% | 780 | 793 |
Idaho's counties show varied growth patterns from 2020 to 2026. Boundary County leads with 3.32% annualized growth, followed by Canyon County (3.3%) and Bonner County (2.95%). The largest counties are Ada County (554,017), Canyon County (283,192), and Kootenai County (194,495). Of the 44 counties in Idaho, 43 are growing while just 1 has experienced population decline. Overall, counties averaged 1.52% annualized growth, with total population growing by 1.84% annually.
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