Population of Counties in Illinois (2021)

In 2019, the most highly populated county within the state of Illinois is Cook County, home to the city of Chicago. With a population of 5,180,493, Cook County has seen a decrease in the total population of 0.36% since the last U.S. census was taken in 2010. Following Cook County, other large counties in Illinois are DuPage County (928,589), Lake County (700,832), Will County (692,310), and Kane County (534,216). Kane County reported the most significant population growth, increasing its population by 3.50%.

Illinois Counties with the Fewest Residents

The county with the lowest population in the state of Illinois is Hardin County, which has a population of 3,910. Since the last census in 2010, Hardin County’s population has seen a decrease of 9.35%. Following behind Hardin County, other small counties in Illinois include Pope County (4,212), Calhoun County (4,802), and Scott County (4,926). Illinois has 72 counties with a population of less than 50,000; all but one (Monroe County) experienced a decline in population. Of the 15 counties with fewer than 10,000 residents, Alexander County experienced the most dramatic decrease with a growth rate of -26.15%.

Illinois Counties with Rapid Growth

Kendall County is the fastest-growing county in Illinois with a population growth rate of 10.87% to 127,915 residents. Following Kendall County, Champagne County (4.19%), Monroe County (4.05%), and Kane County (3.5%) also experienced an increase in residents. Only five other counties in Illinois had any increase in population since 2010. The county with the lowest growth rate in Illinois is Alexander County, which has seen a population decrease of 26.15%.

Name 2021 Population Growth Since 2010 Density (mi²)
Cook County5,106,780-1.77%21,682.89
DuPage County914,269-0.40%3,881.90
Lake County690,431-1.95%2,931.50
Will County689,9311.64%2,929.38
Kane County531,7693.04%2,257.84
McHenry County306,820-0.74%1,302.73
Winnebago County280,456-4.96%1,190.79
Madison County260,846-3.14%1,107.53
St. Clair County256,338-5.18%1,088.39
Champaign County209,2313.81%888.37
Sangamon County192,738-2.54%818.35
Peoria County176,297-5.33%748.54
McLean County169,731-0.05%720.66
Rock Island County140,395-4.89%596.10
Kendall County131,53614.01%558.49
Tazewell County130,509-3.67%554.13
Kankakee County109,680-3.30%465.69
LaSalle County107,689-5.39%457.24
DeKalb County105,9930.81%450.04
Macon County103,019-7.01%437.41
Vermilion County73,870-9.52%313.64
Williamson County65,827-0.91%279.50
Adams County65,059-3.13%276.23
Jackson County55,672-7.79%236.38
Whiteside County54,419-6.95%231.06
Boone County53,672-0.79%227.89
Grundy County51,2162.12%217.46
Ogle County50,367-5.70%213.85
Coles County50,205-6.80%213.17
Knox County49,141-7.13%208.65
Henry County48,601-3.67%206.36
Macoupin County44,142-7.65%187.42
Stephenson County43,900-7.78%186.40
Woodford County38,323-0.87%162.72
Franklin County38,017-5.04%161.42
Jefferson County37,636-2.89%159.80
Clinton County37,292-1.46%158.34
Marion County36,853-6.50%156.47
Livingston County35,516-8.59%150.80
Monroe County35,1656.58%149.31
Lee County33,696-6.36%143.07
Effingham County33,662-1.64%142.93
Fulton County33,360-10.02%141.64
Morgan County32,920-7.28%139.78
Bureau County31,966-8.56%135.72
Christian County31,606-9.08%134.20
Randolph County30,992-7.39%131.59
McDonough County29,078-10.90%123.46
Logan County28,030-7.44%119.01
Montgomery County27,860-7.43%118.29
Iroquois County26,374-11.20%111.98
Saline County22,895-8.06%97.21
Jersey County21,729-5.51%92.26
Shelby County21,450-4.04%91.07
Fayette County21,272-3.88%90.32
Jo Daviess County21,043-7.09%89.35
Perry County20,460-8.31%86.87
Douglas County19,479-2.52%82.71
Crawford County18,341-7.37%77.87
Hancock County17,468-8.50%74.17
Edgar County16,763-9.43%71.17
Warren County16,548-6.58%70.26
Piatt County16,300-2.45%69.21
Union County16,295-8.10%69.19
Bond County16,004-10.02%67.95
Wayne County15,993-4.45%67.90
Pike County15,493-5.50%65.78
Lawrence County15,408-9.04%65.42
De Witt County15,326-7.62%65.07
Mercer County15,209-7.31%64.58
Richland County15,149-6.45%64.32
Clark County15,123-7.17%64.21
Carroll County14,287-7.19%60.66
Moultrie County14,207-4.39%60.32
Washington County13,663-7.13%58.01
White County13,375-8.37%56.79
Massac County13,270-13.72%56.34
Clay County13,020-5.83%55.28
Mason County13,011-11.19%55.24
Greene County12,777-8.01%54.25
Ford County12,459-11.52%52.90
Johnson County12,405-1.58%52.67
Menard County12,010-5.40%50.99
Cass County11,817-13.32%50.17
Wabash County11,514-3.37%48.89
Marshall County11,348-10.20%48.18
Cumberland County10,690-3.28%45.39
Jasper County9,582-1.47%40.68
Hamilton County8,052-4.66%34.19
Brown County6,608-4.49%28.06
Schuyler County6,564-12.89%27.87
Henderson County6,544-10.88%27.79
Edwards County6,411-4.80%27.22
Putnam County5,745-4.44%24.39
Alexander County5,201-36.62%22.08
Stark County5,190-13.05%22.04
Pulaski County5,137-16.14%21.81
Scott County4,999-6.16%21.23
Calhoun County4,559-10.54%19.36
Gallatin County4,394-21.16%18.66
Pope County4,163-6.95%17.68
Hardin County3,677-14.86%15.61