Roosevelt County had the highest population under 18 of 56 counties in 2025, at 31.3%. Deer Lodge County had the lowest, at 14.6%. The median was 20.8% and the figure for Montana was 20.2%. Source: the U.S. Census Bureau.
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.
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 Montana by population under 18 using official data, and cite the source.
rank_places {"indicator":"population_0_17_share","level":"province","within":"Montana","limit":10}
GET https://invokely.ai/api/v1/rank?indicator=population_0_17_share&level=province&within=Montana&limit=10
Roosevelt County, with 31.3% in 2025, according to the U.S. Census Bureau.
Which county has the lowest population under 18?
Deer Lodge County, with 14.6% in 2025.
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.