Data / Rankings / Population under 18 / Counties in Montana

Counties in Montana by population under 18

Roosevelt County had the highest population under 18 of 56 counties in 2021, at 32.7%. Petroleum County had the lowest, at 14.2%. The median was 20.9% and the figure for Montana was 21.3%. Source: the U.S. Census Bureau.

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Highest32.7Roosevelt County
Lowest14.2Petroleum County
Median20.956 counties
Montana21.3History

Map of counties, 2021

Beaverhead County: 18.8 %Big Horn County: 32.5 %Blaine County: 29.1 %Broadwater County: 21 %Carbon County: 18.3 %Carter County: 21.9 %Cascade County: 22.2 %Chouteau County: 23.4 %Custer County: 21.9 %Daniels County: 21.8 %Dawson County: 21.5 %Deer Lodge County: 15.3 %Fallon County: 25.8 %Fergus County: 20.9 %Flathead County: 21.9 %Gallatin County: 19.2 %Garfield County: 24.6 %Glacier County: 30.5 %Golden Valley County: 18 %Granite County: 17.7 %Hill County: 27.3 %Jefferson County: 20.4 %Judith Basin County: 19.5 %Lake County: 22.5 %Lewis and Clark County: 21.3 %Liberty County: 23.1 %Lincoln County: 18.6 %McCone County: 20.6 %Madison County: 16.1 %Meagher County: 17.1 %Mineral County: 19.1 %Missoula County: 18.9 %Musselshell County: 20.3 %Park County: 16.8 %Petroleum County: 14.2 %Phillips County: 23.4 %Pondera County: 23.5 %Powder River County: 18.7 %Powell County: 14.4 %Prairie County: 19.7 %Ravalli County: 19.1 %Richland County: 24.1 %Roosevelt County: 32.7 %Rosebud County: 28.1 %Sanders County: 16.9 %Sheridan County: 21 %Silver Bow County: 20 %Stillwater County: 20.8 %Sweet Grass County: 19.6 %Teton County: 23.2 %Toole County: 20.1 %Treasure County: 21.8 %Valley County: 22.4 %Wheatland County: 22.4 %Wibaux County: 20.3 %Yellowstone County: 22.9 %
  • Under 18
  • 18 to 20
  • 20 to 21
  • 21 to 22
  • 22 to 24
  • 24 and over
%, 2021. Source: Invokely calculation with data from U.S. Census Bureau. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2021

Roosevelt County: 32.7 %Roosevelt County32.7Big Horn County: 32.5 %Big Horn County32.5Glacier County: 30.5 %Glacier County30.5Blaine County: 29.1 %Blaine County29.1Rosebud County: 28.1 %Rosebud County28.1Hill County: 27.3 %Hill County27.3Fallon County: 25.8 %Fallon County25.8Garfield County: 24.6 %Garfield County24.6Richland County: 24.1 %Richland County24.1Pondera County: 23.5 %Pondera County23.5Chouteau County: 23.4 %Chouteau County23.4Phillips County: 23.4 %Phillips County23.4Teton County: 23.2 %Teton County23.2Liberty County: 23.1 %Liberty County23.1Yellowstone County: 22.9 %Yellowstone County22.9Lake County: 22.5 %Lake County22.5Wheatland County: 22.4 %Wheatland County22.4Valley County: 22.4 %Valley County22.4Cascade County: 22.2 %Cascade County22.2Custer County: 21.9 %Custer County21.9Carter County: 21.9 %Carter County21.9Flathead County: 21.9 %Flathead County21.9Treasure County: 21.8 %Treasure County21.8Daniels County: 21.8 %Daniels County21.8Dawson County: 21.5 %Dawson County21.5Lewis and Clark County: 21.3 %Lewis and Clark County21.3Sheridan County: 21 %Sheridan County21Broadwater County: 21 %Broadwater County21Fergus County: 20.9 %Fergus County20.9Stillwater County: 20.8 %Stillwater County20.8McCone County: 20.6 %McCone County20.6Jefferson County: 20.4 %Jefferson County20.4Musselshell County: 20.3 %Musselshell County20.3Wibaux County: 20.3 %Wibaux County20.3Toole County: 20.1 %Toole County20.1Silver Bow County: 20 %Silver Bow County20Prairie County: 19.7 %Prairie County19.7Sweet Grass County: 19.6 %Sweet Grass County19.6Judith Basin County: 19.5 %Judith Basin County19.5Gallatin County: 19.2 %Gallatin County19.2Mineral County: 19.1 %Mineral County19.1Ravalli County: 19.1 %Ravalli County19.1Missoula County: 18.9 %Missoula County18.9Beaverhead County: 18.8 %Beaverhead County18.8Powder River County: 18.7 %Powder River County18.7Lincoln County: 18.6 %Lincoln County18.6Carbon County: 18.3 %Carbon County18.3Golden Valley County: 18 %Golden Valley County18Granite County: 17.7 %Granite County17.7Meagher County: 17.1 %Meagher County17.1Sanders County: 16.9 %Sanders County16.9Park County: 16.8 %Park County16.8Madison County: 16.1 %Madison County16.1Deer Lodge County: 15.3 %Deer Lodge County15.3Powell County: 14.4 %Powell County14.4Petroleum County: 14.2 %Petroleum County14.2Roosevelt County: 32.7 %Roosevelt County32.7Big Horn County: 32.5 %Big Horn County32.5Glacier County: 30.5 %Glacier County30.5Blaine County: 29.1 %Blaine County29.1Rosebud County: 28.1 %Rosebud County28.1Hill County: 27.3 %Hill County27.3Fallon County: 25.8 %Fallon County25.8Garfield County: 24.6 %Garfield County24.6Richland County: 24.1 %Richland County24.1Pondera County: 23.5 %Pondera County23.5Chouteau County: 23.4 %Chouteau County23.4Phillips County: 23.4 %Phillips County23.4Teton County: 23.2 %Teton County23.2Liberty County: 23.1 %Liberty County23.1Yellowstone County: 22.9 %Yellowstone County22.9Lake County: 22.5 %Lake County22.5Wheatland County: 22.4 %Wheatland County22.4Valley County: 22.4 %Valley County22.4Cascade County: 22.2 %Cascade County22.2Custer County: 21.9 %Custer County21.9Carter County: 21.9 %Carter County21.9Flathead County: 21.9 %Flathead County21.9Treasure County: 21.8 %Treasure County21.8Daniels County: 21.8 %Daniels County21.8Dawson County: 21.5 %Dawson County21.5Lewis and Clark County: 21.3 %Lewis and Clark County21.3Sheridan County: 21 %Sheridan County21Broadwater County: 21 %Broadwater County21Fergus County: 20.9 %Fergus County20.9Stillwater County: 20.8 %Stillwater County20.8McCone County: 20.6 %McCone County20.6Jefferson County: 20.4 %Jefferson County20.4Musselshell County: 20.3 %Musselshell County20.3Wibaux County: 20.3 %Wibaux County20.3Toole County: 20.1 %Toole County20.1Silver Bow County: 20 %Silver Bow County20Prairie County: 19.7 %Prairie County19.7Sweet Grass County: 19.6 %Sweet Grass County19.6Judith Basin County: 19.5 %Judith Basin County19.5Gallatin County: 19.2 %Gallatin County19.2Mineral County: 19.1 %Mineral County19.1Ravalli County: 19.1 %Ravalli County19.1Missoula County: 18.9 %Missoula County18.9Beaverhead County: 18.8 %Beaverhead County18.8Powder River County: 18.7 %Powder River County18.7Lincoln County: 18.6 %Lincoln County18.6Carbon County: 18.3 %Carbon County18.3Golden Valley County: 18 %Golden Valley County18Granite County: 17.7 %Granite County17.7Meagher County: 17.1 %Meagher County17.1Sanders County: 16.9 %Sanders County16.9Park County: 16.8 %Park County16.8Madison County: 16.1 %Madison County16.1Deer Lodge County: 15.3 %Deer Lodge County15.3Powell County: 14.4 %Powell County14.4Petroleum County: 14.2 %Petroleum County14.2
%. Source: Invokely calculation with data from U.S. Census Bureau. Retrieved 2026-10-12.

Full ranking

RankCounties2021 (%)Change on 2020
1Roosevelt County32.7+0.6 pts
2Big Horn County32.5-0.8 pts
3Glacier County30.5-0.5 pts
4Blaine County29.1-0.1 pts
5Rosebud County28.1+0.3 pts
6Hill County27.3-0.2 pts
7Fallon County25.8-0.5 pts
8Garfield County24.6+0.4 pts
9Richland County24.1-0.5 pts
10Pondera County23.5-0.2 pts
11Chouteau County23.4-0.5 pts
12Phillips County23.4+0.6 pts
13Teton County23.2-0.7 pts
14Liberty County23.1+0.4 pts
15Yellowstone County22.9-0.2 pts
16Lake County22.5-0.5 pts
17Wheatland County22.4-0.5 pts
18Valley County22.4-0.5 pts
19Cascade County22.2-0.2 pts
20Custer County21.9-0 pts
21Carter County21.9-0.4 pts
22Flathead County21.9-0.1 pts
23Treasure County21.8-1.1 pts
24Daniels County21.8-0.3 pts
25Dawson County21.5-0.1 pts
26Lewis and Clark County21.3-0.3 pts
27Sheridan County21-0.1 pts
28Broadwater County21+0.1 pts
29Fergus County20.9+0.1 pts
30Stillwater County20.8-0 pts
31McCone County20.6-0.1 pts
32Jefferson County20.4-0.4 pts
33Musselshell County20.3+0.4 pts
34Wibaux County20.3-0.2 pts
35Toole County20.1-0.2 pts
36Silver Bow County20-0.2 pts
37Prairie County19.7+0.7 pts
38Sweet Grass County19.6-0.5 pts
39Judith Basin County19.5-0.2 pts
40Gallatin County19.2-0.4 pts
41Mineral County19.1+0.3 pts
42Ravalli County19.1-0.1 pts
43Missoula County18.9-0.3 pts
44Beaverhead County18.8-0.3 pts
45Powder River County18.7+1 pts
46Lincoln County18.6-0 pts
47Carbon County18.3-0.2 pts
48Golden Valley County18+0.8 pts
49Granite County17.7-0.8 pts
50Meagher County17.1-1 pts
51Sanders County16.9-0.6 pts
52Park County16.8-0.1 pts
53Madison County16.1-0.3 pts
54Deer Lodge County15.3-0.3 pts
55Powell County14.4-0.3 pts
56Petroleum County14.2-0.5 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, 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 Montana 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/montana-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 Montana 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/montana-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 Montana 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/montana-counties?period=2021 (Accessed: 12 October 2026).

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

Roosevelt County, with 32.7% in 2021, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Petroleum County, with 14.2% 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.

Population under 18: other rankings

Counties in Montana: more rankings