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 2020, at 28.4%. Pope County had the lowest, at 16.7%. The median was 21.7% and the figure for Illinois was 22%. Source: the U.S. Census Bureau.

Keep it in a collection in your library.
Highest28.4Kendall County
Lowest16.7Pope County
Median21.7102 counties
Illinois22History

Map of counties, 2020

Adams County: 22.4 %Alexander County: 19.2 %Bond County: 18.2 %Boone County: 24.5 %Brown County: 17.3 %Bureau County: 21 %Calhoun County: 20.1 %Carroll County: 18 %Cass County: 24.6 %Champaign County: 19.3 %Christian County: 19.8 %Clark County: 22.4 %Clay County: 22.9 %Clinton County: 21.9 %Coles County: 19.4 %Cook County: 21.1 %Crawford County: 20.1 %Cumberland County: 22.7 %DeKalb County: 22.3 %De Witt County: 21.5 %Douglas County: 24.7 %DuPage County: 22.4 %Edgar County: 20.4 %Edwards County: 22.8 %Effingham County: 23.3 %Fayette County: 20.6 %Ford County: 22.5 %Franklin County: 21.6 %Fulton County: 19.7 %Gallatin County: 19.8 %Greene County: 22.2 %Grundy County: 24.8 %Hamilton County: 22.4 %Hancock County: 21.1 %Hardin County: 17.8 %Henderson County: 18.9 %Henry County: 22.4 %Iroquois County: 22.1 %Jackson County: 19.4 %Jasper County: 22.5 %Jefferson County: 22.3 %Jersey County: 20.5 %Jo Daviess County: 19 %Johnson County: 17.2 %Kane County: 24.9 %Kankakee County: 22.8 %Kendall County: 28.4 %Knox County: 20.1 %Lake County: 23.8 %LaSalle County: 21 %Lawrence County: 19.1 %Lee County: 19.7 %Livingston County: 21.8 %Logan County: 19.5 %McDonough County: 18.3 %McHenry County: 22.9 %McLean County: 21.6 %Macon County: 22.2 %Macoupin County: 20.8 %Madison County: 21.4 %Marion County: 23 %Marshall County: 20.5 %Mason County: 20.2 %Massac County: 22.2 %Menard County: 22.5 %Mercer County: 21.4 %Monroe County: 22.7 %Montgomery County: 20.4 %Morgan County: 19.1 %Moultrie County: 24.2 %Ogle County: 22.6 %Peoria County: 23.4 %Perry County: 19.4 %Piatt County: 22.2 %Pike County: 23 %Pope County: 16.7 %Pulaski County: 20.9 %Putnam County: 19.3 %Randolph County: 20 %Richland County: 22.6 %Rock Island County: 22.2 %St. Clair County: 23.6 %Saline County: 22.1 %Sangamon County: 22 %Schuyler County: 17.9 %Scott County: 21.1 %Shelby County: 21.3 %Stark County: 21.5 %Stephenson County: 21.2 %Tazewell County: 22.5 %Union County: 20.4 %Vermilion County: 23 %Wabash County: 22 %Warren County: 21.7 %Washington County: 21.2 %Wayne County: 23.1 %White County: 20.9 %Whiteside County: 21.8 %Will County: 24.4 %Williamson County: 21.7 %Winnebago County: 23.1 %Woodford County: 24.1 %
  • Under 19
  • 19 to 21
  • 21 to 22
  • 22 to 23
  • 23 and over
%, 2020. Source: Invokely calculation with data from U.S. Census Bureau. Boundaries: U.S. Census Bureau cartographic boundary files.

Top 40 counties, 2020

Kendall County: 28.4 %Kendall County28.4Kane County: 24.9 %Kane County24.9Grundy County: 24.8 %Grundy County24.8Douglas County: 24.7 %Douglas County24.7Cass County: 24.6 %Cass County24.6Boone County: 24.5 %Boone County24.5Will County: 24.4 %Will County24.4Moultrie County: 24.2 %Moultrie County24.2Woodford County: 24.1 %Woodford County24.1Lake County: 23.8 %Lake County23.8St. Clair County: 23.6 %St. Clair County23.6Peoria County: 23.4 %Peoria County23.4Effingham County: 23.3 %Effingham County23.3Wayne County: 23.1 %Wayne County23.1Winnebago County: 23.1 %Winnebago County23.1Vermilion County: 23 %Vermilion County23Pike County: 23 %Pike County23Marion County: 23 %Marion County23Clay County: 22.9 %Clay County22.9McHenry County: 22.9 %McHenry County22.9Edwards County: 22.8 %Edwards County22.8Kankakee County: 22.8 %Kankakee County22.8Cumberland County: 22.7 %Cumberland County22.7Monroe County: 22.7 %Monroe County22.7Ogle County: 22.6 %Ogle County22.6Richland County: 22.6 %Richland County22.6Jasper County: 22.5 %Jasper County22.5Tazewell County: 22.5 %Tazewell County22.5Ford County: 22.5 %Ford County22.5Menard County: 22.5 %Menard County22.5Henry County: 22.4 %Henry County22.4Clark County: 22.4 %Clark County22.4DuPage County: 22.4 %DuPage County22.4Adams County: 22.4 %Adams County22.4Hamilton County: 22.4 %Hamilton County22.4DeKalb County: 22.3 %DeKalb County22.3Jefferson County: 22.3 %Jefferson County22.3Massac County: 22.2 %Massac County22.2Macon County: 22.2 %Macon County22.2Piatt County: 22.2 %Piatt County22.2Kendall County: 28.4 %Kendall County28.4Kane County: 24.9 %Kane County24.9Grundy County: 24.8 %Grundy County24.8Douglas County: 24.7 %Douglas County24.7Cass County: 24.6 %Cass County24.6Boone County: 24.5 %Boone County24.5Will County: 24.4 %Will County24.4Moultrie County: 24.2 %Moultrie County24.2Woodford County: 24.1 %Woodford County24.1Lake County: 23.8 %Lake County23.8St. Clair County: 23.6 %St. Clair County23.6Peoria County: 23.4 %Peoria County23.4Effingham County: 23.3 %Effingham County23.3Wayne County: 23.1 %Wayne County23.1Winnebago County: 23.1 %Winnebago County23.1Vermilion County: 23 %Vermilion County23Pike County: 23 %Pike County23Marion County: 23 %Marion County23Clay County: 22.9 %Clay County22.9McHenry County: 22.9 %McHenry County22.9Edwards County: 22.8 %Edwards County22.8Kankakee County: 22.8 %Kankakee County22.8Cumberland County: 22.7 %Cumberland County22.7Monroe County: 22.7 %Monroe County22.7Ogle County: 22.6 %Ogle County22.6Richland County: 22.6 %Richland County22.6Jasper County: 22.5 %Jasper County22.5Tazewell County: 22.5 %Tazewell County22.5Ford County: 22.5 %Ford County22.5Menard County: 22.5 %Menard County22.5Henry County: 22.4 %Henry County22.4Clark County: 22.4 %Clark County22.4DuPage County: 22.4 %DuPage County22.4Adams County: 22.4 %Adams County22.4Hamilton County: 22.4 %Hamilton County22.4DeKalb County: 22.3 %DeKalb County22.3Jefferson County: 22.3 %Jefferson County22.3Massac County: 22.2 %Massac County22.2Macon County: 22.2 %Macon County22.2Piatt County: 22.2 %Piatt County22.2
%. Source: Invokely calculation with data from U.S. Census Bureau. Retrieved 2026-10-12.

Full ranking

RankCounties2020 (%)Change on 2019
1Kendall County28.4-0.6 pts
2Kane County24.9-0.2 pts
3Grundy County24.8-0.2 pts
4Douglas County24.7-0.1 pts
5Cass County24.6-0 pts
6Boone County24.5-0.6 pts
7Will County24.4-0.4 pts
8Moultrie County24.2-0.7 pts
9Woodford County24.1-0.4 pts
10Lake County23.8-0.3 pts
11St. Clair County23.6+0.1 pts
12Peoria County23.4+0.2 pts
13Effingham County23.3+0.1 pts
14Wayne County23.1-0.1 pts
15Winnebago County23.1+0.1 pts
16Vermilion County23+0.1 pts
17Pike County23+0.3 pts
18Marion County23+0.2 pts
19Clay County22.9+0.2 pts
20McHenry County22.9-0.3 pts
21Edwards County22.8-0.3 pts
22Kankakee County22.8-0.1 pts
23Cumberland County22.7+0.2 pts
24Monroe County22.7-0 pts
25Ogle County22.6-0.1 pts
26Richland County22.6+0.2 pts
27Jasper County22.5-0.1 pts
28Tazewell County22.5-0.2 pts
29Ford County22.5+0.2 pts
30Menard County22.5+0.2 pts
31Henry County22.4-0.4 pts
32Clark County22.40 pts
33DuPage County22.4-0.1 pts
34Adams County22.4+0.1 pts
35Hamilton County22.40 pts
36DeKalb County22.3-0.2 pts
37Jefferson County22.3+0.1 pts
38Massac County22.2-0.2 pts
39Macon County22.2+0.1 pts
40Piatt County22.2+0.1 pts
41Greene County22.2-0 pts
42Rock Island County22.2+0.1 pts
43Saline County22.1-0.1 pts
44Iroquois County22.1-0 pts
45Wabash County22+0.2 pts
46Sangamon County22-0 pts
47Clinton County21.9+0.2 pts
48Livingston County21.8-0 pts
49Whiteside County21.8+0.1 pts
50Warren County21.7+0.6 pts
51Williamson County21.7-0.1 pts
52McLean County21.6-0.1 pts
53Franklin County21.6+0.1 pts
54Stark County21.5-0.3 pts
55De Witt County21.5+0.1 pts
56Madison County21.40 pts
57Mercer County21.4-0.4 pts
58Shelby County21.3+0.1 pts
59Washington County21.2+0.1 pts
60Stephenson County21.2-0.1 pts
61Hancock County21.1-0 pts
62Cook County21.1-0 pts
63Scott County21.1-0.4 pts
64Bureau County21-0.1 pts
65LaSalle County21-0.2 pts
66Pulaski County20.9+0.3 pts
67White County20.9-0.1 pts
68Macoupin County20.8-0.1 pts
69Fayette County20.6-0.1 pts
70Marshall County20.5-0.1 pts
71Jersey County20.5-0.2 pts
72Union County20.40 pts
73Montgomery County20.40 pts
74Edgar County20.4-0.5 pts
75Mason County20.2-0.1 pts
76Crawford County20.1-0.1 pts
77Calhoun County20.1-0.6 pts
78Knox County20.1+0.1 pts
79Randolph County20+0.3 pts
80Christian County19.8-0.2 pts
81Gallatin County19.8-0.5 pts
82Lee County19.70 pts
83Fulton County19.7-0.1 pts
84Logan County19.5-0.1 pts
85Jackson County19.4+0.3 pts
86Perry County19.4-0 pts
87Coles County19.4-0 pts
88Champaign County19.30 pts
89Putnam County19.3-0.1 pts
90Alexander County19.2-1.4 pts
91Morgan County19.1-0.7 pts
92Lawrence County19.1-0.3 pts
93Jo Daviess County19-0.1 pts
94Henderson County18.9+0.2 pts
95McDonough County18.3-0.1 pts
96Bond County18.2-0 pts
97Carroll County18+0.1 pts
98Schuyler County17.9-0.8 pts
99Hardin County17.80 pts
100Brown County17.3+0.6 pts
101Johnson County17.20 pts
102Pope County16.7-1.6 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, 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 Illinois 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/illinois-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 Illinois 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/illinois-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 Illinois 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/illinois-counties?period=2020 (Accessed: 12 October 2026).

BibTeX
@misc{census_counties_in_illinois_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 Illinois 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/illinois-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 Illinois 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/illinois-counties?period=2020
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/population-under-18/illinois-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  -
Embed this chart

Paste this code into a web page or a blog post. The chart shows the latest figures as they are published, with the source and a link back to this page.

Sites that read oEmbed links, such as WordPress, can show the chart when you paste the link to this page.

Use this data in your AI agent

Invokely serves this figure to AI assistants through MCP and to code through a REST API, with the source and citation attached. Ask your assistant:

Rank Counties in Illinois by population under 18 using official data, and cite the source.
rank_places {"indicator":"population_0_17_share","level":"province","within":"Illinois","limit":10}
GET https://invokely.ai/api/v1/rank?indicator=population_0_17_share&level=province&within=Illinois&limit=10

Connect Claude, ChatGPT or Cursor in one step. The trial answers 25 calls a day without an account.

Questions

Which county has the highest population under 18?

Kendall County, with 28.4% in 2020, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Pope County, with 16.7% 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 Illinois: more rankings