Counties in Washington by population under 18

Adams County had the highest population under 18 of 39 counties in 2021, at 33.9%. Jefferson County had the lowest, at 11.8%. The median was 20.7% and the figure for Washington was 21.6%. Source: the U.S. Census Bureau.

Highest33.9Adams County

Lowest11.8Jefferson County

Median20.739 counties

Washington21.6History

Map of counties, 2021

Under 17
17 to 19
19 to 21
21 to 22
22 to 23
23 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	Adams County	33.9	-0 pts
2	Franklin County	31.2	-0.5 pts
3	Grant County	28.3	-0.3 pts
4	Yakima County	28.3	-0.3 pts
5	Benton County	25.9	-0.3 pts
6	Douglas County	24.4	-0.6 pts
7	Pierce County	22.9	-0.2 pts
8	Clark County	22.8	-0.5 pts
9	Cowlitz County	22.5	-0.2 pts
10	Snohomish County	22.4	-0.3 pts
11	Garfield County	22.4	+1.1 pts
12	Lewis County	22.2	-0 pts
13	Chelan County	22	-0.5 pts
14	Okanogan County	21.9	-0.1 pts
15	Spokane County	21.6	-0.2 pts
16	Thurston County	21.3	-0.3 pts
17	Stevens County	21.3	0 pts
18	Lincoln County	21.3	+0.1 pts
19	Skagit County	21.2	-0.3 pts
20	Walla Walla County	20.7	-0 pts
21	Asotin County	20.3	-0.1 pts
22	King County	19.9	-0.2 pts
23	Grays Harbor County	19.9	-0.2 pts
24	Kitsap County	19.8	-0.6 pts
25	Pend Oreille County	19.4	-0 pts
26	Whatcom County	19.4	-0.2 pts
27	Mason County	19.1	-0.1 pts
28	Klickitat County	19.1	-0.4 pts
29	Ferry County	18.6	-0.4 pts
30	Kittitas County	18.2	+0.4 pts
31	Skamania County	17.9	-0.5 pts
32	Island County	17.6	-0.5 pts
33	Whitman County	17.4	+1.8 pts
34	Columbia County	16.7	-0.4 pts
35	Pacific County	16.4	-0.4 pts
36	Clallam County	16.2	-0.2 pts
37	Wahkiakum County	16	-0.9 pts
38	San Juan County	13.7	-0.1 pts
39	Jefferson County	11.8	-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 Washington 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 Washington 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/washington-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 Washington 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/washington-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 Washington 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/washington-counties?period=2021 (Accessed: 12 October 2026).

BibTeX

@misc{census_counties_in_washington_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 Washington 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/washington-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 Washington 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/washington-counties?period=2021
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/population-under-18/washington-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?

Adams County, with 33.9% in 2021, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Jefferson County, with 11.8% 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.