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 2024, at 26.4%. Pope County had the lowest, at 15.1%. The median was 21.1% and the figure for Illinois was 20.9%. Source: the U.S. Census Bureau.

Highest26.4Kendall County
Lowest15.1Pope County
Median21.1102 counties
Illinois20.9History

Top 40 counties, 2024

Kendall County: 26.4 %Kendall County26.4Douglas County: 24.7 %Douglas County24.7Moultrie County: 23.9 %Moultrie County23.9Cass County: 23.8 %Cass County23.8Woodford County: 23.4 %Woodford County23.4Grundy County: 23.3 %Grundy County23.3Pike County: 23.2 %Pike County23.2Peoria County: 23.2 %Peoria County23.2Effingham County: 23 %Effingham County23Kane County: 23 %Kane County23Boone County: 23 %Boone County23Jasper County: 22.9 %Jasper County22.9Vermilion County: 22.8 %Vermilion County22.8Wayne County: 22.8 %Wayne County22.8Will County: 22.7 %Will County22.7Marion County: 22.7 %Marion County22.7Winnebago County: 22.7 %Winnebago County22.7Ford County: 22.5 %Ford County22.5Clay County: 22.5 %Clay County22.5St. Clair County: 22.4 %St. Clair County22.4Cumberland County: 22.3 %Cumberland County22.3Lake County: 22.2 %Lake County22.2Macon County: 22.1 %Macon County22.1Kankakee County: 22.1 %Kankakee County22.1Hamilton County: 22 %Hamilton County22Rock Island County: 22 %Rock Island County22Stark County: 22 %Stark County22Piatt County: 21.9 %Piatt County21.9Jefferson County: 21.9 %Jefferson County21.9Clark County: 21.9 %Clark County21.9McHenry County: 21.8 %McHenry County21.8Adams County: 21.8 %Adams County21.8Monroe County: 21.8 %Monroe County21.8Warren County: 21.7 %Warren County21.7Ogle County: 21.7 %Ogle County21.7Menard County: 21.7 %Menard County21.7Clinton County: 21.6 %Clinton County21.6Greene County: 21.6 %Greene County21.6Richland County: 21.5 %Richland County21.5Henry County: 21.5 %Henry County21.5
%. Source: Invokely calculation with data from U.S. Census Bureau. Retrieved 2026-10-12.

Full ranking

RankCounties2024 (%)Change on 2023
1Kendall County26.4-0.5 pts
2Douglas County24.7-0.1 pts
3Moultrie County23.9-0.2 pts
4Cass County23.8-0.1 pts
5Woodford County23.4-0.2 pts
6Grundy County23.3-0.4 pts
7Pike County23.2-0.2 pts
8Peoria County23.2-0.1 pts
9Effingham County23-0.1 pts
10Kane County23-0.5 pts
11Boone County23-0.5 pts
12Jasper County22.9+0.1 pts
13Vermilion County22.8-0 pts
14Wayne County22.80 pts
15Will County22.7-0.4 pts
16Marion County22.7-0.3 pts
16Winnebago County22.7-0.2 pts
18Ford County22.5-0.1 pts
19Clay County22.5-0.2 pts
20St. Clair County22.4-0.4 pts
21Cumberland County22.3+0.1 pts
22Lake County22.2-0.5 pts
23Macon County22.1-0 pts
24Kankakee County22.1-0.3 pts
25Hamilton County22-0.6 pts
26Rock Island County220 pts
27Stark County22+0.3 pts
28Piatt County21.9-0 pts
29Jefferson County21.9-0.1 pts
30Clark County21.9-0.3 pts
31McHenry County21.8-0.4 pts
32Adams County21.8-0.3 pts
32Monroe County21.8-0.3 pts
34Warren County21.7-0.2 pts
35Ogle County21.7-0.3 pts
36Menard County21.7-0.2 pts
37Clinton County21.6-0 pts
38Greene County21.6-0.4 pts
39Richland County21.5-0.4 pts
40Henry County21.5-0.3 pts
41Franklin County21.50 pts
42Livingston County21.5-0.1 pts
43Whiteside County21.4-0.1 pts
44DuPage County21.4-0.2 pts
45Tazewell County21.4-0.3 pts
46DeKalb County21.4-0.3 pts
47Shelby County21.2-0.1 pts
48Iroquois County21.2-0 pts
49Edwards County21.2-0.2 pts
50Sangamon County21.1-0.2 pts
51Wabash County21.1-0.3 pts
52De Witt County21.1-0.2 pts
53Saline County21-0.1 pts
54Mercer County20.9-0.2 pts
55White County20.8-0.3 pts
56Madison County20.8-0.2 pts
57Hancock County20.8-0.4 pts
58Stephenson County20.7-0.2 pts
59Fayette County20.7-0 pts
60LaSalle County20.6-0.2 pts
61Williamson County20.5-0.4 pts
62Edgar County20.5-0.1 pts
63Pulaski County20.40 pts
64Marshall County20.4+0.1 pts
65Massac County20.4-0.6 pts
66Union County20.4+0.2 pts
67McLean County20.4-0.3 pts
68Washington County20.2-0.3 pts
69Macoupin County20.1-0.1 pts
70Bureau County20-0.2 pts
71Scott County20+0.3 pts
72Lawrence County19.8-0.3 pts
73Knox County19.8-0.3 pts
74Cook County19.7-0.3 pts
74Randolph County19.7-0.2 pts
76Calhoun County19.7-0.7 pts
77Mason County19.70 pts
78Montgomery County19.6-0.5 pts
79Jersey County19.6-0.2 pts
80Crawford County19.6+0.1 pts
81Jackson County19.4-0.2 pts
82Morgan County19.2-0.1 pts
83Coles County19.2-0.1 pts
84Logan County19.1-0.2 pts
85Hardin County19.1-0 pts
86Lee County19.1-0.4 pts
87McDonough County19.1+0.4 pts
88Christian County18.9-0.2 pts
89Henderson County18.9+0.2 pts
90Fulton County18.9-0.2 pts
91Alexander County18.8-1 pts
92Champaign County18.7-0.1 pts
93Gallatin County18.7-0.3 pts
94Putnam County18.6-0.3 pts
95Perry County18.4-0.2 pts
96Jo Daviess County17.9-0.1 pts
97Bond County17.5-0.3 pts
98Schuyler County17.5-0.1 pts
99Carroll County17.4-0.4 pts
100Johnson County16.4-0.2 pts
101Brown County16.2-0.3 pts
102Pope County15.1-0.4 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, 2024) [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, 2024. 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=2024. 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, 2024. 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=2024.

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, 2024 [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=2024 (Accessed: 12 October 2026).

BibTeX
@misc{census_counties_in_illinois_by_2024,
  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, 2024}},
  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=2024. 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, 2024
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=2024
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/population-under-18/illinois-counties?period=2024.
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 26.4% in 2024, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Pope County, with 15.1% in 2024.

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