Data / Rankings / Population under 18 / Counties in Illinois

Counties in Illinois by population under 18

Kendall County had the highest population under 18 of 102 counties in 2021, at 27.8%. Pope County had the lowest, at 16.5%. The median was 21.5% and the figure for Illinois was 21.7%. Source: the U.S. Census Bureau.

Highest27.8Kendall County
Lowest16.5Pope County
Median21.5102 counties
Illinois21.7History

Top 40 counties, 2021

Kendall County: 27.8 %Kendall County27.8Douglas County: 24.6 %Douglas County24.6Cass County: 24.5 %Cass County24.5Moultrie County: 24.5 %Moultrie County24.5Grundy County: 24.4 %Grundy County24.4Kane County: 24.4 %Kane County24.4Boone County: 24.1 %Boone County24.1Woodford County: 23.8 %Woodford County23.8Will County: 23.8 %Will County23.8St. Clair County: 23.4 %St. Clair County23.4Pike County: 23.4 %Pike County23.4Peoria County: 23.3 %Peoria County23.3Lake County: 23.3 %Lake County23.3Effingham County: 23.3 %Effingham County23.3Marion County: 23.2 %Marion County23.2Wayne County: 23 %Wayne County23Winnebago County: 23 %Winnebago County23Vermilion County: 22.9 %Vermilion County22.9Clay County: 22.8 %Clay County22.8Ford County: 22.7 %Ford County22.7Richland County: 22.6 %Richland County22.6Jasper County: 22.6 %Jasper County22.6McHenry County: 22.6 %McHenry County22.6Kankakee County: 22.5 %Kankakee County22.5Clark County: 22.5 %Clark County22.5Cumberland County: 22.5 %Cumberland County22.5Hamilton County: 22.4 %Hamilton County22.4Monroe County: 22.3 %Monroe County22.3Tazewell County: 22.3 %Tazewell County22.3Ogle County: 22.3 %Ogle County22.3Henry County: 22.3 %Henry County22.3Adams County: 22.2 %Adams County22.2Macon County: 22.2 %Macon County22.2Greene County: 22.2 %Greene County22.2Edwards County: 22.2 %Edwards County22.2Rock Island County: 22.1 %Rock Island County22.1Menard County: 22.1 %Menard County22.1DeKalb County: 22.1 %DeKalb County22.1Piatt County: 22.1 %Piatt County22.1Jefferson County: 22.1 %Jefferson County22.1
%. Source: Invokely calculation with data from U.S. Census Bureau. Retrieved 2026-10-12.

Full ranking

RankCounties2021 (%)Change on 2020
1Kendall County27.8-0.6 pts
2Douglas County24.6-0.1 pts
3Cass County24.5-0.1 pts
4Moultrie County24.5+0.3 pts
5Grundy County24.4-0.4 pts
6Kane County24.4-0.5 pts
7Boone County24.1-0.5 pts
8Woodford County23.8-0.3 pts
9Will County23.8-0.5 pts
10St. Clair County23.4-0.2 pts
11Pike County23.4+0.3 pts
12Peoria County23.3-0.1 pts
13Lake County23.3-0.5 pts
14Effingham County23.3-0 pts
15Marion County23.2+0.2 pts
16Wayne County23-0.1 pts
17Winnebago County23-0.1 pts
18Vermilion County22.9-0.1 pts
19Clay County22.8-0.1 pts
20Ford County22.7+0.2 pts
21Richland County22.6+0.1 pts
22Jasper County22.6+0.1 pts
23McHenry County22.6-0.3 pts
24Kankakee County22.5-0.3 pts
25Clark County22.5+0.1 pts
26Cumberland County22.5-0.3 pts
27Hamilton County22.4-0 pts
28Monroe County22.3-0.3 pts
29Tazewell County22.3-0.2 pts
30Ogle County22.3-0.3 pts
31Henry County22.3-0.1 pts
32Adams County22.2-0.1 pts
33Macon County22.20 pts
34Greene County22.20 pts
35Edwards County22.2-0.7 pts
36Rock Island County22.1-0.1 pts
37Menard County22.1-0.4 pts
38DeKalb County22.1-0.2 pts
39Piatt County22.1-0.1 pts
40Jefferson County22.1-0.2 pts
41DuPage County22-0.4 pts
42Saline County21.8-0.3 pts
43Livingston County21.8-0.1 pts
44Sangamon County21.7-0.3 pts
45Wabash County21.7-0.3 pts
46Clinton County21.7-0.1 pts
47Massac County21.7-0.5 pts
48Whiteside County21.7-0.1 pts
49Warren County21.6-0.1 pts
50Iroquois County21.6-0.4 pts
51Williamson County21.5-0.1 pts
52De Witt County21.5-0 pts
53Franklin County21.4-0.2 pts
54Shelby County21.3-0 pts
55McLean County21.3-0.3 pts
56Madison County21.3-0.2 pts
57Stark County21.3-0.2 pts
58Hancock County21.20 pts
59Mercer County21.2-0.2 pts
60White County21.1+0.3 pts
61Stephenson County21-0.2 pts
62Fayette County21+0.4 pts
63Washington County21-0.2 pts
64LaSalle County20.9-0.1 pts
65Cook County20.8-0.3 pts
66Pulaski County20.8-0.1 pts
67Bureau County20.7-0.3 pts
68Macoupin County20.6-0.2 pts
69Crawford County20.4+0.3 pts
70Scott County20.4-0.7 pts
71Edgar County20.3-0 pts
72Jersey County20.2-0.3 pts
73Marshall County20.2-0.3 pts
74Calhoun County20.2+0.1 pts
75Montgomery County20.1-0.2 pts
76Union County20.1-0.3 pts
77Mason County20-0.2 pts
78Knox County20-0.1 pts
79Randolph County19.9-0.1 pts
80Alexander County19.7+0.5 pts
81Lee County19.7-0 pts
82Logan County19.7+0.2 pts
83Christian County19.6-0.2 pts
84Jackson County19.6+0.1 pts
85Perry County19.4-0 pts
86Fulton County19.4-0.3 pts
87Gallatin County19.3-0.4 pts
88Champaign County19.2-0.1 pts
89Henderson County19.2+0.2 pts
90Coles County19.1-0.3 pts
91Putnam County19.1-0.1 pts
92Lawrence County18.9-0.1 pts
93Morgan County18.9-0.2 pts
94Jo Daviess County18.4-0.6 pts
95Bond County18.1-0.1 pts
96McDonough County18.1-0.2 pts
97Schuyler County18+0.2 pts
98Hardin County17.80 pts
99Carroll County17.7-0.3 pts
100Brown County17.1-0.2 pts
101Johnson County16.5-0.7 pts
102Pope County16.5-0.2 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 Illinois 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 Illinois 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/illinois-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 Illinois 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/illinois-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 Illinois 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/illinois-counties?period=2021 (Accessed: 12 October 2026).

BibTeX
@misc{census_counties_in_illinois_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 Illinois 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/illinois-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 Illinois 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/illinois-counties?period=2021
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/population-under-18/illinois-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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Rank Counties in Illinois by population under 18 using official data, and cite the source.
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Questions

Which county has the highest population under 18?

Kendall County, with 27.8% in 2021, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Pope County, with 16.5% 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 Illinois: more rankings