Illinois Population By Age Group and Age Cohort in 2021 (ACS-5Yrs)

Updated on February 28, 2025.

Based on the US Census ACS-5Yrs estimates, in 2021, among the 12.82M Illinois population, the 25-29yrs age group constituted the highest percentage of the total population (6.87%), followed by the 30-34yrs age group (6.79%), and the 55-59yrs age group (6.78%).

In the case of age cohorts, Adults (18-64yrs) constituted the highest percentage of the total population (61.78%), followed by Children (0-17yrs) (22.52%), and Seniors (65yrs and Over) (15.70%).

The first and second charts below shows the percentage of the population by age group and age cohort respectively. The table below also shows the number and percentages for each age group and age cohort.

You can see similar information for other states, and the United States.

Related Topics: Illinois ACS-5Yrs Estimates, 2021 Topic List.

Data Source: US Census - ACS 5-Year Estimates.

Illinois Percentages of Population By Age Group in 2021

25-29yrs

30-34yrs

55-59yrs

35-39yrs

15-19yrs

10-14yrs

20-24yrs

50-54yrs

60-64yrs

40-44yrs

Illinois Percentages of Population By Age Cohort in 2021

Adults (18-64yrs)

Children (0-17yrs)

Seniors (65yrs and Over)

Illinois Population By Age Group in 2021

Items per page:

0 of 0

Age Group	Number of People	% of Total
25-29yrs	880487	6.87
30-34yrs	871055	6.79
55-59yrs	869497	6.78
35-39yrs	863527	6.74
15-19yrs	850104	6.63
10-14yrs	846355	6.60
20-24yrs	833461	6.50
50-54yrs	827372	6.45
60-64yrs	813900	6.35
40-44yrs	813194	6.34
45-49yrs	813111	6.34
5-9yrs	781334	6.09
Under 5yrs	745681	5.82
65-69yrs	671496	5.24
70-74yrs	518791	4.05
75-79yrs	339908	2.65
85yrs and Over	255197	1.99
80-84yrs	227343	1.77

Illinois Population By Age Cohort in 2021

Items per page:

0 of 0

Age Cohort	Number of People	% of Total
Adults (18-64yrs)	7921727	61.78
Children (0-17yrs)	2887351	22.52
Seniors (65yrs and Over)	2012735	15.70