Counties in Idaho by population under 18

Jefferson County had the highest population under 18 of 44 counties in 2017, at 34.7%. Custer County had the lowest, at 16.7%. The median was 25.8% and the figure for Idaho was 26%. Source: the U.S. Census Bureau.

Highest34.7Jefferson County

Lowest16.7Custer County

Median25.844 counties

Idaho26History

Map of counties, 2017

Under 20
20 to 23
23 to 26
26 to 28
28 to 30
30 and over

%, 2017. Source: Invokely calculation with data from U.S. Census Bureau. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2017

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

Full ranking

Rank	Counties	2017 (%)	Change on 2016
1	Jefferson County	34.7	-0.3 pts
2	Franklin County	33.1	-0.4 pts
3	Cassia County	31.8	-0.5 pts
4	Bingham County	31.5	-0.1 pts
5	Bonneville County	31.1	-0.2 pts
6	Jerome County	31	-0.1 pts
7	Power County	30.9	+0.1 pts
8	Lincoln County	30.7	-0.6 pts
9	Caribou County	29.6	+0.2 pts
10	Canyon County	29.5	-0.4 pts
11	Oneida County	28.8	+0.1 pts
12	Minidoka County	28.8	0 pts
13	Fremont County	28.7	-0.2 pts
14	Gooding County	28.4	+0.4 pts
15	Twin Falls County	28.1	+0.1 pts
16	Owyhee County	28	+0.2 pts
17	Bear Lake County	27.7	+0.4 pts
18	Clark County	27.6	-0.6 pts
19	Teton County	27.2	-0.7 pts
20	Payette County	27.1	-0.4 pts
21	Bannock County	26.7	-0.1 pts
22	Butte County	25.9	+0.3 pts
23	Elmore County	25.8	+0.3 pts
24	Ada County	24.7	-0.3 pts
25	Gem County	24.1	-0 pts
26	Boundary County	23.9	+0.1 pts
27	Washington County	23.9	-0.3 pts
28	Kootenai County	23.3	-0.2 pts
29	Benewah County	22.8	0 pts
30	Blaine County	22.6	-0.4 pts
31	Camas County	22.4	+0.1 pts
32	Lewis County	22.4	-0 pts
33	Madison County	22.1	-0.6 pts
34	Nez Perce County	21.6	-0.1 pts
35	Bonner County	20	+0.1 pts
36	Idaho County	19.7	0 pts
37	Latah County	19.5	-0.1 pts
38	Shoshone County	19.4	+0.1 pts
39	Lemhi County	19	+0.2 pts
40	Valley County	18.9	0 pts
41	Adams County	18.1	+1.3 pts
41	Boise County	18.1	+0.3 pts
43	Clearwater County	17	-0.3 pts
44	Custer County	16.7	+0.2 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, 2017) [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, 2017. 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=2017. 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, 2017. 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=2017.

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, 2017 [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=2017 (Accessed: 12 October 2026).

BibTeX

@misc{census_counties_in_idaho_by_2017,
  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, 2017}},
  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=2017. 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, 2017
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=2017
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/population-under-18/idaho-counties?period=2017.
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 34.7% in 2017, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Custer County, with 16.7% in 2017.

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.