| County | Rank | Change (2020) ↓ | 2026 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Camas County | 1 | 24.42% | 1,345 | 1,081 |
| Canyon County | 2 | 21.37% | 282,802 | 233,001 |
| Boundary County | 3 | 16.45% | 14,138 | 12,141 |
| Bonner County | 4 | 16.41% | 55,190 | 47,411 |
| Jefferson County | 5 | 14.99% | 35,738 | 31,080 |
| Gem County | 6 | 14.64% | 22,096 | 19,275 |
| Teton County | 7 | 14.17% | 13,403 | 11,740 |
| Adams County | 8 | 13.41% | 5,016 | 4,423 |
| Kootenai County | 9 | 13.04% | 195,330 | 172,797 |
| Oneida County | 10 | 12.93% | 5,154 | 4,564 |
| Franklin County | 11 | 12.83% | 16,116 | 14,284 |
| Boise County | 12 | 12.03% | 8,584 | 7,662 |
| Ada County | 13 | 11.8% | 557,057 | 498,263 |
| Washington County | 14 | 10.59% | 11,674 | 10,556 |
| Bonneville County | 15 | 10.44% | 137,749 | 124,730 |
| Butte County | 16 | 10.03% | 2,840 | 2,581 |
| Benewah County | 17 | 9.92% | 10,530 | 9,580 |
| Custer County | 18 | 9.86% | 4,690 | 4,269 |
| Payette County | 19 | 9.35% | 27,969 | 25,577 |
| Twin Falls County | 20 | 9.13% | 98,611 | 90,365 |
| Jerome County | 21 | 8.93% | 26,436 | 24,269 |
| Lincoln County | 22 | 8.53% | 5,575 | 5,137 |
| Valley County | 23 | 8.48% | 12,845 | 11,841 |
| Shoshone County | 24 | 7.85% | 14,234 | 13,198 |
| Idaho County | 25 | 7.73% | 17,875 | 16,592 |
| Cassia County | 26 | 7.4% | 26,584 | 24,753 |
| Lemhi County | 27 | 7.35% | 8,540 | 7,955 |
| Bingham County | 28 | 6.74% | 51,340 | 48,097 |
| Minidoka County | 29 | 6.58% | 23,095 | 21,669 |
| Bear Lake County | 30 | 6.06% | 6,751 | 6,365 |
| Latah County | 31 | 5.84% | 41,946 | 39,633 |
| Bannock County | 32 | 5.63% | 92,213 | 87,294 |
| Gooding County | 33 | 5.41% | 16,493 | 15,647 |
| Fremont County | 34 | 4.84% | 14,070 | 13,420 |
| Owyhee County | 35 | 4.71% | 12,558 | 11,993 |
| Madison County | 36 | 4.62% | 55,396 | 52,950 |
| Lewis County | 37 | 4.56% | 3,695 | 3,534 |
| Blaine County | 38 | 4.08% | 25,333 | 24,341 |
| Caribou County | 39 | 3.84% | 7,282 | 7,013 |
| Clearwater County | 40 | 3.76% | 9,087 | 8,758 |
| Power County | 41 | 3.54% | 8,159 | 7,880 |
| Elmore County | 42 | 2.39% | 29,355 | 28,670 |
| Nez Perce County | 43 | 1.82% | 42,916 | 42,148 |
| Clark County | 44 | -0.88% | 784 | 791 |
Idaho's counties show varied growth patterns from 2020 to 2026. Camas County leads with 3.71% annualized growth, followed by Canyon County (3.28%) and Boundary County (2.57%). The largest counties are Ada County (557,057), Canyon County (282,802), and Kootenai County (195,330). Of the 44 counties in Idaho, 43 are growing while just 1 has experienced population decline. Overall, counties averaged 1.44% annualized growth, with total population growing by 1.8% annually.
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