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 2015, at 30%. Brown County had the lowest, at 16%. The median was 22% and the figure for Illinois was 23%. Source: the U.S. Census Bureau.

Keep it in a collection in your library.
Highest30Kendall County
Lowest16Brown County
Median22102 counties
Illinois23History

Map of counties, 2015

Adams County: 22.7 %Alexander County: 23.3 %Bond County: 18.9 %Boone County: 26.2 %Brown County: 16 %Bureau County: 21.8 %Calhoun County: 20.6 %Carroll County: 18.5 %Cass County: 24.2 %Champaign County: 19.1 %Christian County: 20.8 %Clark County: 22.7 %Clay County: 22.5 %Clinton County: 21.8 %Coles County: 19 %Cook County: 22.2 %Crawford County: 20.4 %Cumberland County: 22.8 %DeKalb County: 22.4 %De Witt County: 22 %Douglas County: 25.4 %DuPage County: 23.2 %Edgar County: 21.3 %Edwards County: 22.5 %Effingham County: 23.6 %Fayette County: 21.2 %Ford County: 23.1 %Franklin County: 22 %Fulton County: 20.2 %Gallatin County: 20.8 %Greene County: 22 %Grundy County: 25.8 %Hamilton County: 22.3 %Hancock County: 21.3 %Hardin County: 19.4 %Henderson County: 19.3 %Henry County: 23 %Iroquois County: 22.3 %Jackson County: 18.4 %Jasper County: 22.7 %Jefferson County: 22 %Jersey County: 21.3 %Jo Daviess County: 19.5 %Johnson County: 17.7 %Kane County: 26.8 %Kankakee County: 23.8 %Kendall County: 30 %Knox County: 19.9 %Lake County: 25.2 %LaSalle County: 21.8 %Lawrence County: 19.2 %Lee County: 20 %Livingston County: 21.9 %Logan County: 19.5 %McDonough County: 17.2 %McHenry County: 24.6 %McLean County: 22.2 %Macon County: 22.3 %Macoupin County: 21.3 %Madison County: 22 %Marion County: 22.9 %Marshall County: 20.2 %Mason County: 20.6 %Massac County: 22.7 %Menard County: 22.2 %Mercer County: 22 %Monroe County: 23.2 %Montgomery County: 20.5 %Morgan County: 20.3 %Moultrie County: 24.8 %Ogle County: 23.2 %Peoria County: 23.6 %Perry County: 19.5 %Piatt County: 22.4 %Pike County: 22.4 %Pope County: 17.5 %Pulaski County: 21.4 %Putnam County: 19.5 %Randolph County: 19.6 %Richland County: 22.3 %Rock Island County: 22.4 %St. Clair County: 23.9 %Saline County: 22.5 %Sangamon County: 22.8 %Schuyler County: 19.7 %Scott County: 22.4 %Shelby County: 21.2 %Stark County: 22.2 %Stephenson County: 21.7 %Tazewell County: 23.2 %Union County: 20.7 %Vermilion County: 23.6 %Wabash County: 22 %Warren County: 21.9 %Washington County: 21.1 %Wayne County: 23 %White County: 21.6 %Whiteside County: 22.5 %Will County: 26.3 %Williamson County: 22.1 %Winnebago County: 23.6 %Woodford County: 24.9 %
  • Under 20
  • 20 to 21
  • 21 to 22
  • 22 to 23
  • 23 and over
%, 2015. Source: Invokely calculation with data from U.S. Census Bureau. Boundaries: U.S. Census Bureau cartographic boundary files.

Top 40 counties, 2015

Kendall County: 30 %Kendall County30Kane County: 26.8 %Kane County26.8Will County: 26.3 %Will County26.3Boone County: 26.2 %Boone County26.2Grundy County: 25.8 %Grundy County25.8Douglas County: 25.4 %Douglas County25.4Lake County: 25.2 %Lake County25.2Woodford County: 24.9 %Woodford County24.9Moultrie County: 24.8 %Moultrie County24.8McHenry County: 24.6 %McHenry County24.6Cass County: 24.2 %Cass County24.2St. Clair County: 23.9 %St. Clair County23.9Kankakee County: 23.8 %Kankakee County23.8Peoria County: 23.6 %Peoria County23.6Vermilion County: 23.6 %Vermilion County23.6Winnebago County: 23.6 %Winnebago County23.6Effingham County: 23.6 %Effingham County23.6Alexander County: 23.3 %Alexander County23.3Monroe County: 23.2 %Monroe County23.2DuPage County: 23.2 %DuPage County23.2Ogle County: 23.2 %Ogle County23.2Tazewell County: 23.2 %Tazewell County23.2Ford County: 23.1 %Ford County23.1Wayne County: 23 %Wayne County23Henry County: 23 %Henry County23Marion County: 22.9 %Marion County22.9Cumberland County: 22.8 %Cumberland County22.8Sangamon County: 22.8 %Sangamon County22.8Clark County: 22.7 %Clark County22.7Massac County: 22.7 %Massac County22.7Adams County: 22.7 %Adams County22.7Jasper County: 22.7 %Jasper County22.7Whiteside County: 22.5 %Whiteside County22.5Edwards County: 22.5 %Edwards County22.5Clay County: 22.5 %Clay County22.5Saline County: 22.5 %Saline County22.5Pike County: 22.4 %Pike County22.4Scott County: 22.4 %Scott County22.4Rock Island County: 22.4 %Rock Island County22.4DeKalb County: 22.4 %DeKalb County22.4Kendall County: 30 %Kendall County30Kane County: 26.8 %Kane County26.8Will County: 26.3 %Will County26.3Boone County: 26.2 %Boone County26.2Grundy County: 25.8 %Grundy County25.8Douglas County: 25.4 %Douglas County25.4Lake County: 25.2 %Lake County25.2Woodford County: 24.9 %Woodford County24.9Moultrie County: 24.8 %Moultrie County24.8McHenry County: 24.6 %McHenry County24.6Cass County: 24.2 %Cass County24.2St. Clair County: 23.9 %St. Clair County23.9Kankakee County: 23.8 %Kankakee County23.8Peoria County: 23.6 %Peoria County23.6Vermilion County: 23.6 %Vermilion County23.6Winnebago County: 23.6 %Winnebago County23.6Effingham County: 23.6 %Effingham County23.6Alexander County: 23.3 %Alexander County23.3Monroe County: 23.2 %Monroe County23.2DuPage County: 23.2 %DuPage County23.2Ogle County: 23.2 %Ogle County23.2Tazewell County: 23.2 %Tazewell County23.2Ford County: 23.1 %Ford County23.1Wayne County: 23 %Wayne County23Henry County: 23 %Henry County23Marion County: 22.9 %Marion County22.9Cumberland County: 22.8 %Cumberland County22.8Sangamon County: 22.8 %Sangamon County22.8Clark County: 22.7 %Clark County22.7Massac County: 22.7 %Massac County22.7Adams County: 22.7 %Adams County22.7Jasper County: 22.7 %Jasper County22.7Whiteside County: 22.5 %Whiteside County22.5Edwards County: 22.5 %Edwards County22.5Clay County: 22.5 %Clay County22.5Saline County: 22.5 %Saline County22.5Pike County: 22.4 %Pike County22.4Scott County: 22.4 %Scott County22.4Rock Island County: 22.4 %Rock Island County22.4DeKalb County: 22.4 %DeKalb County22.4
%. Source: Invokely calculation with data from U.S. Census Bureau. Retrieved 2026-10-12.

Full ranking

RankCounties2015 (%)Change on 2014
1Kendall County30-0.3 pts
2Kane County26.8-0.4 pts
3Will County26.3-0.4 pts
4Boone County26.2-0.3 pts
5Grundy County25.8-0.2 pts
6Douglas County25.4-0.1 pts
7Lake County25.2-0.4 pts
8Woodford County24.9-0.1 pts
9Moultrie County24.8-0 pts
10McHenry County24.6-0.4 pts
11Cass County24.2-0.3 pts
12St. Clair County23.9-0.2 pts
13Kankakee County23.8-0.4 pts
14Peoria County23.6-0 pts
15Vermilion County23.6-0.1 pts
16Winnebago County23.6-0.1 pts
17Effingham County23.6-0 pts
18Alexander County23.3-0.4 pts
19Monroe County23.20 pts
20DuPage County23.2-0.2 pts
21Ogle County23.2-0.2 pts
22Tazewell County23.2-0.2 pts
23Ford County23.10 pts
24Wayne County23+0.1 pts
25Henry County23-0 pts
26Marion County22.9+0.1 pts
27Cumberland County22.8-0.3 pts
28Sangamon County22.8-0.1 pts
29Clark County22.7-0.1 pts
30Massac County22.7+0.2 pts
31Adams County22.70 pts
32Jasper County22.7-0.2 pts
33Whiteside County22.5-0.1 pts
34Edwards County22.5-0.8 pts
35Clay County22.5-0 pts
36Saline County22.5+0.2 pts
37Pike County22.4+0.4 pts
38Scott County22.4+0.3 pts
39Rock Island County22.4-0 pts
40DeKalb County22.4-0 pts
41Piatt County22.4-0.1 pts
42Richland County22.30 pts
43Iroquois County22.3-0 pts
44Hamilton County22.3-0.3 pts
45Macon County22.3-0.1 pts
46Menard County22.2-0.6 pts
47Stark County22.2+0.5 pts
48Cook County22.2-0.2 pts
49McLean County22.2-0 pts
50Williamson County22.1+0.3 pts
51De Witt County22+0.3 pts
52Mercer County22-0.2 pts
53Jefferson County22+0.3 pts
54Franklin County22-0.1 pts
55Madison County22-0.1 pts
56Greene County22-0.1 pts
57Wabash County22+0.4 pts
58Livingston County21.9-0.1 pts
59Warren County21.9-0.4 pts
60LaSalle County21.8-0.1 pts
61Bureau County21.8-0.1 pts
62Clinton County21.8+0.1 pts
63Stephenson County21.7-0.2 pts
64White County21.6+0.2 pts
65Pulaski County21.4-0.5 pts
66Macoupin County21.3-0.3 pts
67Jersey County21.3-0.5 pts
68Edgar County21.3-0.2 pts
69Hancock County21.30 pts
70Shelby County21.2-0.4 pts
71Fayette County21.2-0.2 pts
72Washington County21.1-0.1 pts
73Gallatin County20.8+0.5 pts
74Christian County20.8-0.3 pts
75Union County20.7+0.1 pts
76Calhoun County20.6-0.5 pts
77Mason County20.6-0.2 pts
78Montgomery County20.50 pts
79Crawford County20.4+0.3 pts
80Morgan County20.3+0.2 pts
81Marshall County20.2-0 pts
82Fulton County20.2-0.1 pts
83Lee County20-0.2 pts
84Knox County19.9-0.1 pts
85Schuyler County19.7-0.2 pts
86Randolph County19.6-0.1 pts
87Jo Daviess County19.5-0.1 pts
88Putnam County19.5-0.2 pts
89Perry County19.5-0.1 pts
90Logan County19.5+0.1 pts
91Hardin County19.4-0.6 pts
92Henderson County19.3+0.1 pts
93Lawrence County19.2+0.2 pts
94Champaign County19.1-0 pts
95Coles County19+0.3 pts
96Bond County18.9-0.4 pts
97Carroll County18.5-0.2 pts
98Jackson County18.40 pts
99Johnson County17.7+0.2 pts
100Pope County17.5-0.4 pts
101McDonough County17.2+0.2 pts
102Brown County16+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 Illinois by population under 18, 2015) [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, 2015. 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=2015. 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, 2015. 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=2015.

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, 2015 [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=2015 (Accessed: 12 October 2026).

BibTeX
@misc{census_counties_in_illinois_by_2015,
  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, 2015}},
  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=2015. 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, 2015
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=2015
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/population-under-18/illinois-counties?period=2015.
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 30% in 2015, according to the U.S. Census Bureau.

Which county has the lowest population under 18?

Brown County, with 16% in 2015.

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