Counties in Idaho by population under 18

Jefferson County had the highest population under 18 of 44 counties in 2020, at 33.7%. Clearwater County had the lowest, at 16.2%. The median was 25.1% and the figure for Idaho was 25%. Source: the U.S. Census Bureau.

Highest33.7Jefferson County

Lowest16.2Clearwater County

Median25.144 counties

Idaho25History

All counties, 2020

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

Full ranking

Rank	Counties	2020 (%)	Change on 2019
1	Jefferson County	33.7	-0.5 pts
2	Franklin County	31.7	-0.4 pts
3	Cassia County	30.9	-0.5 pts
4	Bonneville County	30.4	-0 pts
5	Bingham County	30.3	-0.6 pts
6	Jerome County	30.2	-0.5 pts
7	Power County	30	-0.3 pts
8	Caribou County	29.3	-0.7 pts
9	Minidoka County	28.8	-0 pts
10	Canyon County	27.9	-0.5 pts
11	Gooding County	27.8	+0.3 pts
12	Lincoln County	27.7	-0.5 pts
13	Clark County	27.6	+2.3 pts
14	Oneida County	27.3	-1.5 pts
15	Bear Lake County	27.3	-0.2 pts
16	Twin Falls County	27.2	-0.3 pts
17	Fremont County	27	-0.6 pts
18	Owyhee County	26.8	-0.4 pts
19	Payette County	26.2	-0.4 pts
20	Bannock County	26.2	-0.1 pts
21	Teton County	25.3	-0.9 pts
22	Butte County	25.2	-0.6 pts
23	Elmore County	25	-0.6 pts
24	Boundary County	23.6	+0.4 pts
25	Gem County	23.6	-0.1 pts
26	Ada County	23.3	-0.6 pts
27	Washington County	23.3	-0.3 pts
28	Kootenai County	22.7	-0.2 pts
29	Benewah County	21.9	-0.4 pts
30	Nez Perce County	21.3	-0.1 pts
31	Lewis County	21.3	+0.9 pts
32	Blaine County	20.7	-0.7 pts
33	Madison County	20.6	-0.3 pts
34	Camas County	19.9	-1.2 pts
35	Idaho County	19.6	-0 pts
36	Bonner County	19.5	-0.2 pts
37	Shoshone County	19.4	+0.1 pts
38	Latah County	19.4	-0.2 pts
39	Valley County	18.6	-0.2 pts
40	Lemhi County	18.6	-0.5 pts
41	Custer County	17.2	+0.2 pts
42	Adams County	17.1	-0.2 pts
43	Boise County	16.5	-0.5 pts
44	Clearwater County	16.2	-0.3 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, 2020) [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, 2020. 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=2020. 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, 2020. 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=2020.

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, 2020 [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=2020 (Accessed: 12 October 2026).

BibTeX

@misc{census_counties_in_idaho_by_2020,
  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, 2020}},
  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=2020. 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, 2020
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=2020
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/population-under-18/idaho-counties?period=2020.
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 33.7% in 2020, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Clearwater County, with 16.2% in 2020.

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.