Population of Counties in Illinois (2020)

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 2020 Population Growth Since 2010
Cook County5,180,493-0.36%
DuPage County928,5891.15%
Lake County700,832-0.48%
Will County692,3101.99%
Kane County534,2163.50%
McHenry County308,570-0.16%
Winnebago County284,081-3.73%
Madison County264,461-1.81%
St. Clair County261,059-3.43%
Champaign County209,9834.19%
Sangamon County195,348-1.22%
Peoria County180,621-3.01%
McLean County172,8281.78%
Rock Island County143,477-2.80%
Tazewell County132,328-2.33%
Kendall County127,91510.87%
Kankakee County110,024-2.99%
LaSalle County109,430-3.85%
Macon County104,712-5.48%
DeKalb County104,143-0.95%
Vermilion County76,806-5.92%
Williamson County67,0560.94%
Adams County65,691-2.19%
Jackson County57,419-4.90%
Whiteside County55,626-4.88%
Boone County53,577-0.97%
Grundy County50,9721.64%
Ogle County50,923-4.68%
Coles County50,885-5.54%
Knox County50,112-5.29%
Henry County49,090-2.70%
Macoupin County45,313-5.20%
Stephenson County44,753-5.99%
Franklin County38,701-3.33%
Woodford County38,463-0.54%
Jefferson County37,820-2.42%
Clinton County37,639-0.53%
Marion County37,620-4.56%
Livingston County35,761-7.97%
Fulton County34,844-6.01%
Monroe County34,3354.05%
Lee County34,223-4.87%
Effingham County34,208-0.04%
Morgan County33,976-4.31%
Bureau County32,993-5.62%
Christian County32,661-6.05%
Randolph County32,106-4.06%
McDonough County29,955-8.19%
Logan County28,925-4.49%
Montgomery County28,601-4.96%
Iroquois County27,604-7.06%
Saline County23,906-4.00%
Jersey County21,847-4.89%
Shelby County21,741-2.76%
Fayette County21,416-3.23%
Jo Daviess County21,366-5.66%
Perry County21,174-5.11%
Douglas County19,479-2.52%
Crawford County18,807-5.02%
Hancock County17,844-6.53%
Edgar County17,360-6.20%
Warren County17,032-3.88%
Union County16,841-5.04%
Bond County16,630-6.50%
Piatt County16,396-1.87%
Wayne County16,332-2.43%
De Witt County15,769-4.95%
Lawrence County15,765-6.94%
Richland County15,763-2.66%
Pike County15,611-4.78%
Mercer County15,601-4.93%
Clark County15,596-4.27%
Moultrie County14,717-0.96%
Carroll County14,312-7.02%
Massac County14,080-8.45%
Washington County13,995-4.87%
White County13,665-6.40%
Mason County13,565-7.41%
Ford County13,264-5.80%
Clay County13,253-4.15%
Greene County13,044-6.09%
Johnson County12,456-1.21%
Menard County12,288-3.21%
Cass County12,260-10.10%
Wabash County11,549-3.08%
Marshall County11,534-8.67%
Cumberland County10,808-2.22%
Jasper County9,611-1.17%
Hamilton County8,163-3.35%
Schuyler County6,907-8.33%
Henderson County6,709-8.63%
Brown County6,556-5.25%
Edwards County6,392-5.08%
Alexander County6,060-26.15%
Putnam County5,740-4.52%
Pulaski County5,463-10.76%
Stark County5,427-9.10%
Gallatin County5,058-9.26%
Scott County4,926-7.53%
Calhoun County4,802-5.77%
Pope County4,212-5.77%
Hardin County3,910-9.45%