| County | Rank | Change (2020) ↓ | 2025 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Boundary County | 1 | 18.63% | 14,403 | 12,141 |
| Canyon County | 2 | 18.03% | 275,042 | 233,031 |
| Bonner County | 3 | 16.43% | 55,201 | 47,411 |
| Camas County | 4 | 16.42% | 1,262 | 1,084 |
| Gem County | 5 | 15.83% | 22,330 | 19,278 |
| Adams County | 6 | 15.21% | 5,098 | 4,425 |
| Jefferson County | 7 | 14.05% | 35,449 | 31,082 |
| Teton County | 8 | 12.77% | 13,232 | 11,734 |
| Boise County | 9 | 12.25% | 8,602 | 7,663 |
| Benewah County | 10 | 11.26% | 10,658 | 9,579 |
| Kootenai County | 11 | 10.77% | 191,409 | 172,791 |
| Lincoln County | 12 | 10.36% | 5,668 | 5,136 |
| Franklin County | 13 | 10.34% | 15,760 | 14,283 |
| Payette County | 14 | 9.58% | 28,040 | 25,588 |
| Washington County | 15 | 9.56% | 11,570 | 10,560 |
| Oneida County | 16 | 9.49% | 4,997 | 4,564 |
| Jerome County | 17 | 9.35% | 26,538 | 24,268 |
| Ada County | 18 | 9.35% | 544,908 | 498,301 |
| Custer County | 19 | 9.23% | 4,663 | 4,269 |
| Valley County | 20 | 9.14% | 12,924 | 11,842 |
| Bonneville County | 21 | 8.88% | 135,813 | 124,736 |
| Fremont County | 22 | 8.35% | 14,540 | 13,419 |
| Twin Falls County | 23 | 8.01% | 97,614 | 90,374 |
| Idaho County | 24 | 7.87% | 17,896 | 16,590 |
| Latah County | 25 | 7.65% | 42,669 | 39,638 |
| Power County | 26 | 7.33% | 8,461 | 7,883 |
| Bingham County | 27 | 6.82% | 51,380 | 48,099 |
| Shoshone County | 28 | 6.6% | 14,076 | 13,205 |
| Bear Lake County | 29 | 6.41% | 6,775 | 6,367 |
| Owyhee County | 30 | 6.13% | 12,734 | 11,999 |
| Madison County | 31 | 5.79% | 55,975 | 52,912 |
| Cassia County | 32 | 5.57% | 26,135 | 24,755 |
| Minidoka County | 33 | 5.47% | 22,856 | 21,671 |
| Lewis County | 34 | 5.45% | 3,716 | 3,524 |
| Butte County | 35 | 5.42% | 2,723 | 2,583 |
| Lemhi County | 36 | 4.89% | 8,347 | 7,958 |
| Bannock County | 37 | 4.76% | 91,435 | 87,281 |
| Blaine County | 38 | 4.1% | 25,342 | 24,345 |
| Clearwater County | 39 | 4.09% | 9,110 | 8,752 |
| Gooding County | 40 | 3.88% | 16,265 | 15,657 |
| Elmore County | 41 | 3.74% | 29,752 | 28,680 |
| Caribou County | 42 | 3.26% | 7,245 | 7,016 |
| Nez Perce County | 43 | 1.35% | 42,716 | 42,148 |
| Clark County | 44 | -0.76% | 787 | 793 |
Idaho's counties show varied growth patterns from 2020 to 2025. Boundary County leads with 18.63% annualized growth, followed by Canyon County (18.03%) and Bonner County (16.43%). The largest counties are Ada County (544,908), Canyon County (275,042), and Kootenai County (191,409). Of the 44 counties in Idaho, 43 are growing while just 1 has experienced population decline. Overall, counties averaged 8.62% annualized growth, with total population growing by 9.88% annually.
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