Population Characteristics - Age
(2020)
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| County Name | Under 18
Rank | Under 18 | 18 - 64 | 65 and over | Dependency ratio |
| Jefferson | 1 | 32.9% | 54.9% | 12.2% | 82.3 |
| Cassia | 2 | 31.0% | 54.3% | 14.7% | 84.2 |
| Franklin | 3 | 30.9% | 54.4% | 14.6% | 83.7 |
| Power | 4 | 30.5% | 52.8% | 16.7% | 89.5 |
| Bonneville | 5 | 30.3% | 55.9% | 13.7% | 78.8 |
| Jerome | 6 | 30.0% | 56.5% | 13.5% | 76.9 |
| Bingham | 7 | 29.9% | 55.3% | 14.8% | 80.8 |
| Minidoka | 8 | 28.8% | 54.9% | 16.3% | 82.3 |
| Caribou | 9 | 28.2% | 53.9% | 17.9% | 85.6 |
| Canyon | 10 | 27.3% | 58.3% | 14.5% | 71.6 |
| Oneida | 11 | 27.2% | 52.1% | 20.7% | 91.8 |
| Gooding | 12 | 27.0% | 54.6% | 18.5% | 83.3 |
| Twin Falls | 13 | 26.9% | 56.8% | 16.2% | 75.9 |
| Lincoln | 14 | 26.9% | 57.9% | 15.3% | 72.8 |
| Madison | 15 | 26.6% | 65.9% | 7.5% | 51.7 |
| Bear Lake | 16 | 26.5% | 52.3% | 21.3% | 91.3 |
| Payette | 17 | 25.7% | 55.2% | 19.2% | 81.3 |
| Bannock | 18 | 25.5% | 59.3% | 15.1% | 68.6 |
| Owyhee | 19 | 25.0% | 56.9% | 18.1% | 75.8 |
| Elmore | 20 | 25.0% | 60.7% | 14.3% | 64.6 |
| Fremont | 21 | 24.2% | 57.8% | 18.0% | 73.0 |
| Teton | 22 | 23.2% | 63.6% | 13.1% | 57.2 |
| Butte | 23 | 23.2% | 51.4% | 25.4% | 94.4 |
| Boundary | 24 | 23.1% | 52.9% | 24.0% | 89.1 |
| Clark | 25 | 23.0% | 57.4% | 19.6% | 74.2 |
| Ada | 26 | 22.7% | 61.8% | 15.5% | 61.9 |
| Gem | 27 | 22.6% | 54.6% | 22.8% | 83.1 |
| Kootenai | 28 | 22.4% | 57.8% | 19.7% | 73.0 |
| Washington | 29 | 22.4% | 51.3% | 26.3% | 94.9 |
| Camas | 30 | 22.3% | 54.3% | 23.4% | 84.0 |
| Benewah | 31 | 21.9% | 54.8% | 23.4% | 82.6 |
| Lewis | 32 | 21.8% | 49.8% | 28.4% | 100.8 |
| Nez Perce | 33 | 21.3% | 58.0% | 20.7% | 72.4 |
| Blaine | 34 | 20.4% | 58.9% | 20.7% | 69.8 |
| Shoshone | 35 | 20.2% | 55.5% | 24.3% | 80.1 |
| Idaho | 36 | 19.3% | 51.6% | 29.1% | 93.9 |
| Bonner | 37 | 19.3% | 54.7% | 26.0% | 82.8 |
| Latah | 38 | 18.2% | 67.1% | 14.7% | 49.1 |
| Lemhi | 39 | 18.1% | 50.0% | 31.8% | 100.0 |
| Valley | 40 | 17.8% | 55.3% | 26.9% | 80.9 |
| Adams | 41 | 16.9% | 52.2% | 30.9% | 91.6 |
| Custer | 42 | 16.8% | 51.5% | 31.7% | 94.0 |
| Boise | 43 | 15.6% | 56.6% | 27.8% | 76.6 |
| Clearwater | 44 | 15.4% | 56.0% | 28.6% | 78.5 |
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