Counties in Idaho by population under 18

Jefferson County had the highest population under 18 of 44 counties in 2015, at 35%. Custer County had the lowest, at 16.9%. The median was 25.8% and the figure for Idaho was 26.5%. Source: the U.S. Census Bureau.

Highest35Jefferson County

Lowest16.9Custer County

Median25.844 counties

Idaho26.5History

All counties, 2015

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

Full ranking

Rank	Counties	2015 (%)	Change on 2014
1	Jefferson County	35	-0.1 pts
2	Franklin County	33.9	-0.4 pts
3	Cassia County	32.5	-0.1 pts
4	Bingham County	31.8	-0.2 pts
5	Lincoln County	31.5	-0.3 pts
6	Bonneville County	31.3	-0.1 pts
7	Jerome County	31.2	+0.1 pts
8	Power County	31	+0.2 pts
9	Canyon County	30.2	-0.2 pts
10	Fremont County	29.4	-0.3 pts
11	Caribou County	29.2	-0.2 pts
12	Minidoka County	28.9	-0.1 pts
13	Oneida County	28.7	+0.8 pts
14	Teton County	28.5	-0.1 pts
15	Gooding County	28.5	-0.3 pts
16	Twin Falls County	28	+0.2 pts
17	Owyhee County	27.7	0 pts
18	Bear Lake County	27.7	-0.2 pts
19	Clark County	27.6	-2.1 pts
20	Payette County	27.4	0 pts
21	Bannock County	27.1	-0 pts
22	Elmore County	25.8	-0.7 pts
23	Butte County	25.7	-0.3 pts
24	Ada County	25.4	-0.2 pts
25	Washington County	23.9	-0.1 pts
26	Gem County	23.8	-0.3 pts
27	Boundary County	23.7	+0.4 pts
28	Kootenai County	23.6	-0.2 pts
29	Madison County	23.5	-0.4 pts
30	Blaine County	23.3	+0.1 pts
31	Camas County	22.6	-1.8 pts
32	Benewah County	22.3	+0.2 pts
33	Lewis County	22	-0.3 pts
34	Nez Perce County	21.6	-0.2 pts
35	Idaho County	20.2	+0.2 pts
36	Bonner County	20.2	-0.3 pts
37	Latah County	19.5	+0.4 pts
38	Shoshone County	19.5	-0.1 pts
39	Valley County	18.6	-0.2 pts
40	Lemhi County	18.5	-0.2 pts
41	Boise County	18.3	-0.6 pts
42	Adams County	17	+0.3 pts
43	Clearwater County	17	-0.3 pts
44	Custer County	16.9	-0.8 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, 2015) [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, 2015. 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=2015. 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, 2015. 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=2015.

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, 2015 [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=2015 (Accessed: 12 October 2026).

BibTeX

@misc{census_counties_in_idaho_by_2015,
  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, 2015}},
  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=2015. 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, 2015
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=2015
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/population-under-18/idaho-counties?period=2015.
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 35% in 2015, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Custer County, with 16.9% in 2015.

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.