Data / Population under 18 / Jefferson County

Population under 18 in Jefferson County

Population under 18 in Jefferson County was 19.9% in 2025, according to the U.S. Census Bureau. That is down 0.3 pts from 2024. That is the 35th highest of 56 counties in 2025.

202519.9%
Change on 2024-0.3 pts
Rank35th of 56Counties in Montana ranked
Series high22.92010
Series low19.92025
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Population under 18 in Jefferson County, 2010 to 2025

19202122232010201320162019202220252010: 22.9 %2011: 22 %2012: 21.6 %2013: 21.6 %2014: 21.4 %2015: 20.9 %2016: 20.8 %2017: 20.9 %2018: 20.9 %2019: 20.7 %2020: 20.8 %2021: 20.4 %2022: 20.8 %2023: 20.7 %2024: 20.3 %2025: 19.9 %
%. Source: Invokely calculation with data from U.S. Census Bureau. Retrieved 2026-10-12, published 2026-06-25.
All 16 values
Period%
202519.9
202420.3
202320.7
202220.8
202120.4
202020.8
201920.7
201820.9
201720.9
201620.8
201520.9
201421.4
201321.6
201221.6
201122
201022.9

Compared with Montana and United States

Place2025
Jefferson County19.9
Montana20.2
United States21.1

Rankings

Definition

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.

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 (Population under 18, Jefferson County, 2010 to 2025) [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, Population under 18, Jefferson County, 2010 to 2025. U.S. Census Bureau, 25 June 2026, https://www.census.gov/programs-surveys/popest/data/data-sets.html. Invokely, https://invokely.ai/en/population-under-18/jefferson-county-montana. 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. Population under 18, Jefferson County, 2010 to 2025. Dataset. Accessed October 12, 2026. https://www.census.gov/programs-surveys/popest/data/data-sets.html. Also distributed by Invokely, https://invokely.ai/en/population-under-18/jefferson-county-montana.

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, Population under 18, Jefferson County, 2010 to 2025 [Dataset]. Available at: https://www.census.gov/programs-surveys/popest/data/data-sets.html, via Invokely: https://invokely.ai/en/population-under-18/jefferson-county-montana (Accessed: 12 October 2026).

BibTeX
@misc{census_population_under_18_jefferson_2025,
  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: Population under 18, Jefferson County, 2010 to 2025}},
  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/en/population-under-18/jefferson-county-montana. 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: Population under 18, Jefferson County, 2010 to 2025
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/en/population-under-18/jefferson-county-montana
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/en/population-under-18/jefferson-county-montana.
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

What is the population under 18 in Jefferson County?

Population under 18 in Jefferson County was 19.9% in 2025, according to the U.S. Census Bureau. That is down 0.3 pts from 2024. That is the 35th highest of 56 counties in 2025.

Where does this figure come from?

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 by Invokely on 2026-10-12.

What was the highest population under 18 in Jefferson County?

22.9% in 2010, the highest value since 2010 in this series.

Related statistics for Jefferson County

All statistics for Jefferson County | Jefferson County in figures