Counties in Idaho by population under 18

Jefferson County had the highest population under 18 of 44 counties in 2018, at 34.6%. Clearwater County had the lowest, at 16.9%. The median was 25.7% and the figure for Idaho was 25.7%. Source: the U.S. Census Bureau.

Highest34.6Jefferson County

Lowest16.9Clearwater County

Median25.744 counties

Idaho25.7History

Map of counties, 2018

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

%, 2018. Source: Invokely calculation with data from U.S. Census Bureau. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2018

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

Full ranking

Rank	Counties	2018 (%)	Change on 2017
1	Jefferson County	34.6	-0.1 pts
2	Franklin County	32.4	-0.7 pts
3	Cassia County	31.7	-0.1 pts
4	Bingham County	31.3	-0.2 pts
5	Power County	31	+0.1 pts
6	Jerome County	30.9	-0.1 pts
7	Bonneville County	30.7	-0.3 pts
8	Caribou County	29.9	+0.3 pts
9	Lincoln County	29.7	-0.9 pts
10	Oneida County	29.1	+0.3 pts
11	Canyon County	28.9	-0.5 pts
12	Minidoka County	28.6	-0.1 pts
13	Fremont County	28.5	-0.2 pts
14	Gooding County	28.1	-0.3 pts
15	Twin Falls County	27.7	-0.4 pts
16	Owyhee County	27.7	-0.3 pts
17	Bear Lake County	27.3	-0.4 pts
18	Payette County	26.9	-0.2 pts
19	Teton County	26.6	-0.5 pts
20	Bannock County	26.4	-0.3 pts
21	Butte County	26.1	+0.2 pts
22	Clark County	25.8	-1.8 pts
23	Elmore County	25.5	-0.2 pts
24	Ada County	24.3	-0.4 pts
25	Gem County	23.8	-0.3 pts
26	Washington County	23.7	-0.2 pts
27	Boundary County	23.6	-0.4 pts
28	Kootenai County	23.1	-0.2 pts
29	Camas County	23.1	+0.6 pts
30	Benewah County	22.6	-0.2 pts
31	Blaine County	22.2	-0.3 pts
32	Madison County	21.4	-0.7 pts
33	Nez Perce County	21.4	-0.3 pts
34	Lewis County	21.1	-1.3 pts
35	Shoshone County	19.9	+0.4 pts
36	Idaho County	19.8	+0.1 pts
37	Latah County	19.8	+0.2 pts
38	Bonner County	19.7	-0.3 pts
39	Lemhi County	19	0 pts
40	Valley County	18.8	-0.1 pts
41	Adams County	17.9	-0.2 pts
42	Boise County	17.5	-0.6 pts
43	Custer County	17.1	+0.4 pts
44	Clearwater County	16.9	-0.1 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, 2018) [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, 2018. 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=2018. 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, 2018. 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=2018.

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, 2018 [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=2018 (Accessed: 12 October 2026).

BibTeX

@misc{census_counties_in_idaho_by_2018,
  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, 2018}},
  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=2018. 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, 2018
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=2018
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/population-under-18/idaho-counties?period=2018.
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  -

Embed this chart

Paste this code into a web page or a blog post. The chart shows the latest figures as they are published, with the source and a link back to this page.

Embed code

<iframe src="https://invokely.ai/embed/rankings/population-under-18/idaho-counties?period=2018" width="760" height="500" title="Counties in Idaho by population under 18, 2018, chart from Invokely" loading="lazy" style="border:0;width:100%;max-width:760px" referrerpolicy="strict-origin-when-cross-origin"></iframe>

Sites that read oEmbed links, such as WordPress, can show the chart when you paste the link to this page.

Use this data in your AI agent

Invokely serves this figure to AI assistants through MCP and to code through a REST API, with the source and citation attached. Ask your assistant:

Rank Counties in Idaho by population under 18 using official data, and cite the source.

rank_places {"indicator":"population_0_17_share","level":"province","within":"Idaho","limit":10}
GET https://invokely.ai/api/v1/rank?indicator=population_0_17_share&level=province&within=Idaho&limit=10

Connect Claude, ChatGPT or Cursor in one step. The trial answers 25 calls a day without an account.

Questions

Which county has the highest population under 18?

Jefferson County, with 34.6% in 2018, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Clearwater County, with 16.9% in 2018.

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.