Counties in Idaho by population under 18

Jefferson County had the highest population under 18 of 44 counties in 2021, at 33.4%. Clearwater County had the lowest, at 16.2%. The median was 24.4% and the figure for Idaho was 24.7%. Source: the U.S. Census Bureau.

Highest33.4Jefferson County

Lowest16.2Clearwater County

Median24.444 counties

Idaho24.7History

Map of counties, 2021

Under 20
20 to 22
22 to 24
24 to 27
27 to 29
29 and over

%, 2021. Source: Invokely calculation with data from U.S. Census Bureau. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2021

%. Source: Invokely calculation with data from U.S. Census Bureau. Retrieved 2026-10-12.

Full ranking

Rank	Counties	2021 (%)	Change on 2020
1	Jefferson County	33.4	-0.3 pts
2	Franklin County	31.3	-0.4 pts
3	Cassia County	30.8	-0.2 pts
4	Bonneville County	30.1	-0.3 pts
5	Bingham County	30	-0.3 pts
6	Power County	29.8	-0.2 pts
7	Jerome County	29.8	-0.4 pts
8	Caribou County	29.1	-0.2 pts
9	Minidoka County	28.4	-0.4 pts
10	Bear Lake County	27.6	+0.3 pts
11	Clark County	27.6	0 pts
12	Canyon County	27.5	-0.5 pts
13	Lincoln County	27.2	-0.5 pts
14	Gooding County	27.2	-0.6 pts
15	Twin Falls County	26.9	-0.4 pts
16	Oneida County	26.7	-0.7 pts
17	Owyhee County	26.6	-0.2 pts
18	Fremont County	26.3	-0.7 pts
19	Payette County	26	-0.2 pts
20	Bannock County	25.8	-0.3 pts
21	Elmore County	24.5	-0.5 pts
22	Butte County	24.5	-0.7 pts
23	Teton County	24.3	-0.9 pts
24	Boundary County	23.4	-0.2 pts
25	Washington County	23.1	-0.1 pts
26	Gem County	23	-0.6 pts
27	Ada County	22.9	-0.4 pts
28	Kootenai County	22.6	-0.1 pts
29	Benewah County	22	+0.1 pts
30	Lewis County	21.9	+0.6 pts
31	Nez Perce County	21.1	-0.2 pts
32	Madison County	20.8	+0.1 pts
33	Shoshone County	20.1	+0.7 pts
34	Blaine County	20	-0.8 pts
35	Latah County	19.7	+0.3 pts
36	Bonner County	19.5	0 pts
37	Idaho County	19.5	-0.1 pts
38	Camas County	19.1	-0.8 pts
39	Valley County	18.2	-0.4 pts
40	Lemhi County	18.2	-0.4 pts
41	Adams County	17.1	0 pts
42	Custer County	17.1	-0.1 pts
43	Boise County	16.9	+0.4 pts
44	Clearwater County	16.2	-0 pts

Other periods

About this ranking

Residents aged 0 to 17 as a percentage of total population on 1 July. United States: Census Bureau county population estimates by age; states and the nation are sums of their counties.

Uses the US age of majority. Not comparable with population_0_14_share, which stops at 14.

Every value in the ranking comes from the same publisher and the same period, so the counties are compared on one definition. Equal values share a rank.

How to cite

U.S. Census Bureau. Population Estimates Program, county population by age and sex: residents aged 0 to 17 as a percentage of the total on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage; states and the nation summed from counties. https://www.census.gov/programs-surveys/popest/data/data-sets.html. Retrieved 2026-10-12.

Citation styles

The publisher is the author. Invokely is named only as the place the figures were read, where a style asks for it.

APA 7

U.S. Census Bureau. (2026). Population Estimates Program, county population by age and sex: residents aged 0 to 17 as a percentage of the total on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage; states and the nation summed from counties (Counties in Idaho by population under 18, 2021) [Data set]. Retrieved October 12, 2026, from https://www.census.gov/programs-surveys/popest/data/data-sets.html

MLA 9

Population Estimates Program, county population by age and sex: residents aged 0 to 17 as a percentage of the total on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage; states and the nation summed from counties, Counties in Idaho by population under 18, 2021. U.S. Census Bureau, 25 June 2026, https://www.census.gov/programs-surveys/popest/data/data-sets.html. Invokely, https://invokely.ai/rankings/population-under-18/idaho-counties?period=2021. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Census Bureau. 2026. Population Estimates Program, county population by age and sex: residents aged 0 to 17 as a percentage of the total on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage; states and the nation summed from counties. Counties in Idaho by population under 18, 2021. Dataset. Accessed October 12, 2026. https://www.census.gov/programs-surveys/popest/data/data-sets.html. Also distributed by Invokely, https://invokely.ai/rankings/population-under-18/idaho-counties?period=2021.

Harvard

U.S. Census Bureau (2026) Population Estimates Program, county population by age and sex: residents aged 0 to 17 as a percentage of the total on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage; states and the nation summed from counties, Counties in Idaho by population under 18, 2021 [Dataset]. Available at: https://www.census.gov/programs-surveys/popest/data/data-sets.html, via Invokely: https://invokely.ai/rankings/population-under-18/idaho-counties?period=2021 (Accessed: 12 October 2026).

BibTeX

@misc{census_counties_in_idaho_by_2021,
  author = {{U.S. Census Bureau}},
  title = {{Population Estimates Program, county population by age and sex: residents aged 0 to 17 as a percentage of the total on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage; states and the nation summed from counties: Counties in Idaho by population under 18, 2021}},
  year = {2026},
  howpublished = {Data set},
  url = {https://www.census.gov/programs-surveys/popest/data/data-sets.html},
  urldate = {2026-10-12},
  note = {Accessed via Invokely, https://invokely.ai/rankings/population-under-18/idaho-counties?period=2021. Publisher attribution: U.S. Census Bureau. Population Estimates Program, county population by age and sex: residents aged 0 to 17 as a percentage of the total on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage; states and the nation summed from counties. https://www.census.gov/programs-surveys/popest/data/data-sets.html. Retrieved 2026-10-12.},
}

RIS

TY  - DATA
AU  - U.S. Census Bureau
TI  - Population Estimates Program, county population by age and sex: residents aged 0 to 17 as a percentage of the total on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage; states and the nation summed from counties: Counties in Idaho by population under 18, 2021
PY  - 2026
DA  - 2026/06/25
PB  - U.S. Census Bureau
DB  - Invokely
UR  - https://www.census.gov/programs-surveys/popest/data/data-sets.html
L2  - https://invokely.ai/rankings/population-under-18/idaho-counties?period=2021
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/population-under-18/idaho-counties?period=2021.
N1  - Publisher attribution: U.S. Census Bureau. Population Estimates Program, county population by age and sex: residents aged 0 to 17 as a percentage of the total on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage; states and the nation summed from counties. https://www.census.gov/programs-surveys/popest/data/data-sets.html. Retrieved 2026-10-12.
ER  -

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Questions

Which county has the highest population under 18?

Jefferson County, with 33.4% in 2021, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Clearwater County, with 16.2% in 2021.

Where does this ranking come from?

Every value comes from one source and one period, so the places are comparable: U.S. Census Bureau, Population Estimates Program, county population by age and sex: residents aged 0 to 17 as a percentage of the total on 1 July, 2010 to 2019 from the 2010 to 2020 intercensal file and 2020 onwards from the latest vintage; states and the nation summed from counties. Retrieved 2026-10-12.