Data / Rankings / Population under 18 / Counties in Montana

Counties in Montana by population under 18

Big Horn County had the highest population under 18 of 56 counties in 2020, at 33.3%. Powell County had the lowest, at 14.7%. The median was 20.9% and the figure for Montana was 21.5%. Source: the U.S. Census Bureau.

Highest33.3Big Horn County
Lowest14.7Powell County
Median20.956 counties
Montana21.5History

All counties, 2020

Big Horn County: 33.3 %Big Horn County33.3Roosevelt County: 32.2 %Roosevelt County32.2Glacier County: 31 %Glacier County31Blaine County: 29.2 %Blaine County29.2Rosebud County: 27.8 %Rosebud County27.8Hill County: 27.5 %Hill County27.5Fallon County: 26.3 %Fallon County26.3Richland County: 24.6 %Richland County24.6Garfield County: 24.2 %Garfield County24.2Chouteau County: 23.9 %Chouteau County23.9Teton County: 23.9 %Teton County23.9Pondera County: 23.7 %Pondera County23.7Yellowstone County: 23.1 %Yellowstone County23.1Lake County: 23 %Lake County23Treasure County: 23 %Treasure County23Wheatland County: 22.9 %Wheatland County22.9Valley County: 22.8 %Valley County22.8Phillips County: 22.8 %Phillips County22.8Liberty County: 22.6 %Liberty County22.6Cascade County: 22.4 %Cascade County22.4Carter County: 22.3 %Carter County22.3Daniels County: 22.1 %Daniels County22.1Custer County: 22 %Custer County22Flathead County: 21.9 %Flathead County21.9Lewis and Clark County: 21.6 %Lewis and Clark County21.6Dawson County: 21.6 %Dawson County21.6Sheridan County: 21.1 %Sheridan County21.1Broadwater County: 20.9 %Broadwater County20.9Stillwater County: 20.8 %Stillwater County20.8Jefferson County: 20.8 %Jefferson County20.8Fergus County: 20.8 %Fergus County20.8McCone County: 20.7 %McCone County20.7Wibaux County: 20.5 %Wibaux County20.5Toole County: 20.4 %Toole County20.4Silver Bow County: 20.2 %Silver Bow County20.2Sweet Grass County: 20.2 %Sweet Grass County20.2Musselshell County: 19.9 %Musselshell County19.9Judith Basin County: 19.7 %Judith Basin County19.7Gallatin County: 19.6 %Gallatin County19.6Missoula County: 19.3 %Missoula County19.3Ravalli County: 19.2 %Ravalli County19.2Beaverhead County: 19.1 %Beaverhead County19.1Prairie County: 18.9 %Prairie County18.9Mineral County: 18.8 %Mineral County18.8Lincoln County: 18.6 %Lincoln County18.6Carbon County: 18.5 %Carbon County18.5Granite County: 18.5 %Granite County18.5Meagher County: 18.1 %Meagher County18.1Powder River County: 17.7 %Powder River County17.7Sanders County: 17.5 %Sanders County17.5Golden Valley County: 17.3 %Golden Valley County17.3Park County: 16.9 %Park County16.9Madison County: 16.4 %Madison County16.4Deer Lodge County: 15.6 %Deer Lodge County15.6Petroleum County: 14.7 %Petroleum County14.7Powell County: 14.7 %Powell County14.7
%. Source: Invokely calculation with data from U.S. Census Bureau. Retrieved 2026-10-12.

Full ranking

RankCounties2020 (%)Change on 2019
1Big Horn County33.3-0.4 pts
2Roosevelt County32.2+1.3 pts
3Glacier County31-0.2 pts
4Blaine County29.2+0.1 pts
5Rosebud County27.8+1 pts
6Hill County27.5+1.2 pts
7Fallon County26.3-0.3 pts
8Richland County24.6+0.4 pts
9Garfield County24.2-0.7 pts
10Chouteau County23.9-2.1 pts
11Teton County23.9+0.7 pts
12Pondera County23.7-1 pts
13Yellowstone County23.1-0.2 pts
14Lake County23-0.4 pts
15Treasure County23+0.3 pts
16Wheatland County22.9+2.5 pts
17Valley County22.8-0 pts
18Phillips County22.8-1 pts
19Liberty County22.6-0.7 pts
20Cascade County22.4+0.1 pts
21Carter County22.3-1.4 pts
22Daniels County22.1+0.8 pts
23Custer County22-0.4 pts
24Flathead County21.9-0.1 pts
25Lewis and Clark County21.6+0.1 pts
26Dawson County21.6-0.4 pts
27Sheridan County21.1+0.8 pts
28Broadwater County20.9-1 pts
29Stillwater County20.8+0.5 pts
30Jefferson County20.8+0.1 pts
31Fergus County20.8+0.2 pts
32McCone County20.7-0.6 pts
33Wibaux County20.5-1.5 pts
34Toole County20.4+0.9 pts
35Silver Bow County20.2+0.3 pts
36Sweet Grass County20.2-0.8 pts
37Musselshell County19.9+0.5 pts
38Judith Basin County19.7+1.2 pts
39Gallatin County19.6-0.4 pts
40Missoula County19.3-0.2 pts
41Ravalli County19.2-0.3 pts
42Beaverhead County19.1-0.6 pts
43Prairie County18.9+0.3 pts
44Mineral County18.8+0.9 pts
45Lincoln County18.6+0.3 pts
46Carbon County18.5+0.1 pts
47Granite County18.5+0.6 pts
48Meagher County18.1+0.7 pts
49Powder River County17.7-1.6 pts
50Sanders County17.5-0.7 pts
51Golden Valley County17.3-2.7 pts
52Park County16.9-0.2 pts
53Madison County16.4+0.1 pts
54Deer Lodge County15.6-0.9 pts
55Petroleum County14.7-3.9 pts
56Powell County14.7-0 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 Montana by population under 18, 2020) [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 Montana by population under 18, 2020. 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/montana-counties?period=2020. 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 Montana by population under 18, 2020. 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/montana-counties?period=2020.

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 Montana by population under 18, 2020 [Dataset]. Available at: https://www.census.gov/programs-surveys/popest/data/data-sets.html, via Invokely: https://invokely.ai/rankings/population-under-18/montana-counties?period=2020 (Accessed: 12 October 2026).

BibTeX
@misc{census_counties_in_montana_by_2020,
  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 Montana by population under 18, 2020}},
  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/montana-counties?period=2020. 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 Montana by population under 18, 2020
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/montana-counties?period=2020
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/population-under-18/montana-counties?period=2020.
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?

Big Horn County, with 33.3% in 2020, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Powell County, with 14.7% in 2020.

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.

Population under 18: other rankings

Counties in Montana: more rankings