Population Characteristics - Age
(2021)
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| County Name | Under 18
Rank | Under 18 | 18 - 64 | 65 and over | Dependency ratio |
| Jefferson | 1 | 33.1% | 54.8% | 12.1% | 82.3 |
| Cassia | 2 | 31.0% | 54.3% | 14.7% | 84.3 |
| Franklin | 3 | 30.9% | 54.5% | 14.6% | 83.6 |
| Power | 4 | 30.6% | 53.2% | 16.3% | 88.1 |
| Bonneville | 5 | 30.3% | 56.1% | 13.5% | 78.2 |
| Bingham | 6 | 30.0% | 55.3% | 14.7% | 80.9 |
| Jerome | 7 | 29.6% | 57.0% | 13.3% | 75.3 |
| Minidoka | 8 | 28.9% | 55.0% | 16.2% | 82.0 |
| Caribou | 9 | 28.1% | 53.7% | 18.2% | 86.2 |
| Canyon | 10 | 27.1% | 58.7% | 14.2% | 70.4 |
| Twin Falls | 11 | 27.0% | 56.9% | 16.1% | 75.7 |
| Bear Lake | 12 | 26.9% | 52.8% | 20.3% | 89.3 |
| Oneida | 13 | 26.8% | 51.9% | 21.3% | 92.6 |
| Gooding | 14 | 26.8% | 55.0% | 18.3% | 81.9 |
| Madison | 15 | 26.6% | 65.6% | 7.7% | 52.3 |
| Lincoln | 16 | 26.4% | 58.7% | 14.9% | 70.3 |
| Payette | 17 | 25.9% | 55.2% | 18.9% | 81.1 |
| Bannock | 18 | 25.5% | 59.3% | 15.1% | 68.5 |
| Owyhee | 19 | 25.0% | 57.2% | 17.8% | 74.8 |
| Elmore | 20 | 24.7% | 60.8% | 14.5% | 64.6 |
| Fremont | 21 | 23.8% | 58.4% | 17.8% | 71.3 |
| Clark | 22 | 23.6% | 56.9% | 19.4% | 75.6 |
| Boundary | 23 | 23.1% | 53.6% | 23.3% | 86.7 |
| Butte | 24 | 22.9% | 52.0% | 25.1% | 92.5 |
| Teton | 25 | 22.8% | 63.6% | 13.6% | 57.2 |
| Lewis | 26 | 22.7% | 49.6% | 27.7% | 101.5 |
| Kootenai | 27 | 22.6% | 58.0% | 19.5% | 72.6 |
| Washington | 28 | 22.5% | 51.8% | 25.6% | 93.0 |
| Ada | 29 | 22.5% | 61.9% | 15.6% | 61.6 |
| Benewah | 30 | 22.3% | 54.3% | 23.3% | 84.0 |
| Gem | 31 | 22.2% | 55.4% | 22.4% | 80.5 |
| Camas | 32 | 21.9% | 54.3% | 23.7% | 84.0 |
| Nez Perce | 33 | 21.3% | 57.9% | 20.7% | 72.6 |
| Shoshone | 34 | 21.0% | 55.8% | 23.2% | 79.3 |
| Blaine | 35 | 19.9% | 59.1% | 21.0% | 69.2 |
| Idaho | 36 | 19.6% | 51.5% | 28.9% | 94.1 |
| Bonner | 37 | 19.5% | 54.5% | 25.9% | 83.3 |
| Latah | 38 | 18.9% | 66.4% | 14.7% | 50.6 |
| Lemhi | 39 | 18.0% | 50.6% | 31.4% | 97.6 |
| Valley | 40 | 17.4% | 55.8% | 26.7% | 79.1 |
| Adams | 41 | 17.2% | 51.7% | 31.0% | 93.3 |
| Custer | 42 | 16.4% | 52.6% | 30.9% | 90.0 |
| Boise | 43 | 15.9% | 56.4% | 27.7% | 77.4 |
| Clearwater | 44 | 15.2% | 56.9% | 27.9% | 75.7 |
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