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 2019, at 28.9%. Brown County had the lowest, at 16.7%. The median was 21.7% and the figure for Illinois was 22.1%. Source: the U.S. Census Bureau.

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Highest28.9Kendall County
Lowest16.7Brown County
Median21.7102 counties
Illinois22.1History

Map of counties, 2019

Adams County: 22.3 %Alexander County: 20.6 %Bond County: 18.3 %Boone County: 25.2 %Brown County: 16.7 %Bureau County: 21.2 %Calhoun County: 20.7 %Carroll County: 17.9 %Cass County: 24.6 %Champaign County: 19.2 %Christian County: 20 %Clark County: 22.4 %Clay County: 22.7 %Clinton County: 21.6 %Coles County: 19.4 %Cook County: 21.1 %Crawford County: 20.3 %Cumberland County: 22.5 %DeKalb County: 22.5 %De Witt County: 21.4 %Douglas County: 24.8 %DuPage County: 22.5 %Edgar County: 20.9 %Edwards County: 23.1 %Effingham County: 23.3 %Fayette County: 20.7 %Ford County: 22.3 %Franklin County: 21.5 %Fulton County: 19.8 %Gallatin County: 20.3 %Greene County: 22.2 %Grundy County: 25.1 %Hamilton County: 22.4 %Hancock County: 21.2 %Hardin County: 17.7 %Henderson County: 18.8 %Henry County: 22.8 %Iroquois County: 22.1 %Jackson County: 19.1 %Jasper County: 22.6 %Jefferson County: 22.2 %Jersey County: 20.7 %Jo Daviess County: 19.1 %Johnson County: 17.2 %Kane County: 25.1 %Kankakee County: 22.9 %Kendall County: 28.9 %Knox County: 19.9 %Lake County: 24 %LaSalle County: 21.2 %Lawrence County: 19.3 %Lee County: 19.7 %Livingston County: 21.8 %Logan County: 19.6 %McDonough County: 18.4 %McHenry County: 23.2 %McLean County: 21.7 %Macon County: 22.1 %Macoupin County: 21 %Madison County: 21.4 %Marion County: 22.7 %Marshall County: 20.7 %Mason County: 20.3 %Massac County: 22.5 %Menard County: 22.3 %Mercer County: 21.8 %Monroe County: 22.7 %Montgomery County: 20.4 %Morgan County: 19.8 %Moultrie County: 24.8 %Ogle County: 22.7 %Peoria County: 23.3 %Perry County: 19.5 %Piatt County: 22.1 %Pike County: 22.7 %Pope County: 18.4 %Pulaski County: 20.6 %Putnam County: 19.4 %Randolph County: 19.7 %Richland County: 22.3 %Rock Island County: 22.1 %St. Clair County: 23.5 %Saline County: 22.2 %Sangamon County: 22 %Schuyler County: 18.7 %Scott County: 21.4 %Shelby County: 21.2 %Stark County: 21.7 %Stephenson County: 21.3 %Tazewell County: 22.7 %Union County: 20.4 %Vermilion County: 22.9 %Wabash County: 21.8 %Warren County: 21.1 %Washington County: 21.2 %Wayne County: 23.2 %White County: 20.9 %Whiteside County: 21.7 %Will County: 24.7 %Williamson County: 21.7 %Winnebago County: 23 %Woodford County: 24.5 %
  • Under 20
  • 20 to 21
  • 21 to 22
  • 22 to 23
  • 23 and over
%, 2019. Source: Invokely calculation with data from U.S. Census Bureau. Boundaries: U.S. Census Bureau cartographic boundary files.

Top 40 counties, 2019

Kendall County: 28.9 %Kendall County28.9Boone County: 25.2 %Boone County25.2Grundy County: 25.1 %Grundy County25.1Kane County: 25.1 %Kane County25.1Moultrie County: 24.8 %Moultrie County24.8Douglas County: 24.8 %Douglas County24.8Will County: 24.7 %Will County24.7Cass County: 24.6 %Cass County24.6Woodford County: 24.5 %Woodford County24.5Lake County: 24 %Lake County24St. Clair County: 23.5 %St. Clair County23.5Peoria County: 23.3 %Peoria County23.3Effingham County: 23.3 %Effingham County23.3McHenry County: 23.2 %McHenry County23.2Wayne County: 23.2 %Wayne County23.2Edwards County: 23.1 %Edwards County23.1Winnebago County: 23 %Winnebago County23Kankakee County: 22.9 %Kankakee County22.9Vermilion County: 22.9 %Vermilion County22.9Henry County: 22.8 %Henry County22.8Marion County: 22.7 %Marion County22.7Monroe County: 22.7 %Monroe County22.7Ogle County: 22.7 %Ogle County22.7Tazewell County: 22.7 %Tazewell County22.7Pike County: 22.7 %Pike County22.7Clay County: 22.7 %Clay County22.7Jasper County: 22.6 %Jasper County22.6Cumberland County: 22.5 %Cumberland County22.5DeKalb County: 22.5 %DeKalb County22.5Massac County: 22.5 %Massac County22.5DuPage County: 22.5 %DuPage County22.5Clark County: 22.4 %Clark County22.4Hamilton County: 22.4 %Hamilton County22.4Richland County: 22.3 %Richland County22.3Adams County: 22.3 %Adams County22.3Ford County: 22.3 %Ford County22.3Menard County: 22.3 %Menard County22.3Greene County: 22.2 %Greene County22.2Saline County: 22.2 %Saline County22.2Jefferson County: 22.2 %Jefferson County22.2Kendall County: 28.9 %Kendall County28.9Boone County: 25.2 %Boone County25.2Grundy County: 25.1 %Grundy County25.1Kane County: 25.1 %Kane County25.1Moultrie County: 24.8 %Moultrie County24.8Douglas County: 24.8 %Douglas County24.8Will County: 24.7 %Will County24.7Cass County: 24.6 %Cass County24.6Woodford County: 24.5 %Woodford County24.5Lake County: 24 %Lake County24St. Clair County: 23.5 %St. Clair County23.5Peoria County: 23.3 %Peoria County23.3Effingham County: 23.3 %Effingham County23.3McHenry County: 23.2 %McHenry County23.2Wayne County: 23.2 %Wayne County23.2Edwards County: 23.1 %Edwards County23.1Winnebago County: 23 %Winnebago County23Kankakee County: 22.9 %Kankakee County22.9Vermilion County: 22.9 %Vermilion County22.9Henry County: 22.8 %Henry County22.8Marion County: 22.7 %Marion County22.7Monroe County: 22.7 %Monroe County22.7Ogle County: 22.7 %Ogle County22.7Tazewell County: 22.7 %Tazewell County22.7Pike County: 22.7 %Pike County22.7Clay County: 22.7 %Clay County22.7Jasper County: 22.6 %Jasper County22.6Cumberland County: 22.5 %Cumberland County22.5DeKalb County: 22.5 %DeKalb County22.5Massac County: 22.5 %Massac County22.5DuPage County: 22.5 %DuPage County22.5Clark County: 22.4 %Clark County22.4Hamilton County: 22.4 %Hamilton County22.4Richland County: 22.3 %Richland County22.3Adams County: 22.3 %Adams County22.3Ford County: 22.3 %Ford County22.3Menard County: 22.3 %Menard County22.3Greene County: 22.2 %Greene County22.2Saline County: 22.2 %Saline County22.2Jefferson County: 22.2 %Jefferson County22.2
%. Source: Invokely calculation with data from U.S. Census Bureau. Retrieved 2026-10-12.

Full ranking

RankCounties2019 (%)Change on 2018
1Kendall County28.9-0.2 pts
2Boone County25.2-0.3 pts
3Grundy County25.1-0.3 pts
4Kane County25.1-0.5 pts
5Moultrie County24.8-0.1 pts
6Douglas County24.8-0.4 pts
7Will County24.7-0.4 pts
8Cass County24.6+0.2 pts
9Woodford County24.5-0.1 pts
10Lake County24-0.3 pts
11St. Clair County23.5-0.1 pts
12Peoria County23.3-0.1 pts
13Effingham County23.30 pts
14McHenry County23.2-0.3 pts
15Wayne County23.2+0.1 pts
16Edwards County23.1+0.3 pts
17Winnebago County23-0.1 pts
18Kankakee County22.9-0.1 pts
19Vermilion County22.9-0.3 pts
20Henry County22.8-0.1 pts
21Marion County22.7-0.2 pts
22Monroe County22.7+0.1 pts
23Ogle County22.7-0 pts
24Tazewell County22.7-0.2 pts
25Pike County22.7+0.2 pts
26Clay County22.7-0.3 pts
27Jasper County22.60 pts
28Cumberland County22.50 pts
29DeKalb County22.5+0.1 pts
29Massac County22.5-0.4 pts
31DuPage County22.5-0.2 pts
32Clark County22.4-0.3 pts
33Hamilton County22.4-0.1 pts
34Richland County22.3-0.4 pts
35Adams County22.30 pts
36Ford County22.3-0.4 pts
37Menard County22.3-0.3 pts
38Greene County22.2+0.2 pts
39Saline County22.2-0.1 pts
40Jefferson County22.2+0.1 pts
41Piatt County22.1-0.3 pts
42Macon County22.10 pts
43Rock Island County22.1-0 pts
44Iroquois County22.10 pts
45Sangamon County22-0.2 pts
46Livingston County21.8-0.2 pts
47Wabash County21.8-0.1 pts
48Mercer County21.8-0.2 pts
49Williamson County21.7-0.2 pts
50Stark County21.7+0.1 pts
51McLean County21.7-0.2 pts
52Whiteside County21.7-0.2 pts
53Clinton County21.6-0 pts
54Franklin County21.5-0.2 pts
55Scott County21.4-0.6 pts
56Madison County21.4-0.2 pts
57De Witt County21.4-0.3 pts
58Stephenson County21.3-0.1 pts
59Shelby County21.2-0.1 pts
60LaSalle County21.2-0.3 pts
61Washington County21.2-0.2 pts
62Bureau County21.2-0.4 pts
62Hancock County21.2-0 pts
64Cook County21.1-0.3 pts
65Warren County21.1-0.4 pts
66Macoupin County21-0.2 pts
67White County20.9-0.1 pts
68Edgar County20.9-0.1 pts
69Fayette County20.7-0.2 pts
70Calhoun County20.7-0.3 pts
71Jersey County20.7-0 pts
72Marshall County20.7+0.3 pts
73Pulaski County20.6-0.6 pts
74Alexander County20.6-0.9 pts
75Union County20.4-0.1 pts
76Montgomery County20.4-0.1 pts
77Gallatin County20.3-0.9 pts
78Mason County20.30 pts
79Crawford County20.3+0.2 pts
80Christian County20-0.1 pts
81Knox County19.9+0.1 pts
82Morgan County19.8-0.2 pts
83Fulton County19.8-0.3 pts
84Lee County19.7-0.1 pts
85Randolph County19.7-0.2 pts
86Logan County19.6-0.2 pts
87Perry County19.5-0.1 pts
88Coles County19.4+0.1 pts
89Putnam County19.4-0.3 pts
90Lawrence County19.3+0.3 pts
91Champaign County19.2-0 pts
92Jackson County19.1+0.1 pts
92Jo Daviess County19.1-0.1 pts
94Henderson County18.8+0.2 pts
95Schuyler County18.7+0.1 pts
96McDonough County18.4+0.1 pts
97Pope County18.4+0.2 pts
98Bond County18.3-0.5 pts
99Carroll County17.9-0.2 pts
100Hardin County17.7-0.6 pts
101Johnson County17.2-0.2 pts
102Brown County16.7+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, 2019) [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, 2019. 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=2019. 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, 2019. 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=2019.

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, 2019 [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=2019 (Accessed: 12 October 2026).

BibTeX
@misc{census_counties_in_illinois_by_2019,
  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, 2019}},
  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=2019. 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, 2019
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=2019
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/population-under-18/illinois-counties?period=2019.
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?

Kendall County, with 28.9% in 2019, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Brown County, with 16.7% in 2019.

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