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What are the largest counties in Illinois?

Cook County is the largest county in Illinois, with 5,194,625 residents in 2025 (Census PEP). DuPage County (934,298) and Lake County (719,339) come next.

Data as of 2025 · updated

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All 102 ranked Illinois counties

Illinois counties ranked by population
RankCountyResidents 2025Change 2020–25
1Cook County5,194,625−1.3%
2DuPage County934,298+0.3%
3Lake County719,339+0.8%
4Will County712,253+2.2%
5Kane County525,757+1.8%
6McHenry County317,751+2.5%
7Winnebago County283,674−0.4%
8Madison County263,110−1.0%
9St. Clair County250,708−2.5%
10Champaign County209,972+1.8%
11Sangamon County194,170−1.0%
12Peoria County178,553−1.6%
13McLean County171,419+0.1%
14Kendall County145,470+9.9%
15Rock Island County141,869−1.7%
16Tazewell County130,049−1.0%
17LaSalle County107,773−1.5%
18Kankakee County105,525−1.7%
19DeKalb County101,835+1.5%
20Macon County99,300−4.3%
21Vermilion County71,259−3.7%
22Williamson County67,225+0.1%
23Adams County64,267−2.1%
24Whiteside County54,121−2.6%
25Grundy County54,052+2.9%
26Boone County53,568+0.4%
27Jackson County52,501−1.5%
28Ogle County51,399−0.7%
29Henry County48,095−2.2%
30Knox County47,767−4.1%
31Coles County46,607−1.0%
32Macoupin County43,748−2.6%
33Stephenson County43,220−3.0%
34Woodford County38,111−0.8%
35Clinton County37,128+0.6%
36Franklin County36,916−2.1%
37Marion County36,382−3.4%
38Jefferson County36,147−2.3%
39Livingston County35,057−2.1%
40Monroe County34,840−0.3%
41Effingham County34,519−0.5%
42Christian County33,443−1.5%
43Lee County32,914−3.4%
44Fulton County32,901−2.0%
45Morgan County32,515−2.9%
46Bureau County32,510−2.1%
47Randolph County29,921−0.6%
48Montgomery County28,076−0.6%
49Logan County27,182−2.5%
50Iroquois County26,150−3.0%
51McDonough County25,916−4.5%
52Saline County22,772−4.1%
53Jo Daviess County21,594−2.2%
54Jersey County21,160−1.5%
55Fayette County20,790−3.2%
56Shelby County20,576−1.6%
57Perry County20,160−3.5%
58Douglas County19,880+0.5%
59Crawford County18,648+0.1%
60Bond County16,959+0.6%
61Hancock County16,803−4.4%
62Piatt County16,791+0.6%
63Union County16,656−3.7%
64Edgar County16,323−2.9%
65Warren County16,222−3.7%
66Wayne County15,882−1.6%
67Carroll County15,419−1.7%
68Mercer County15,229−2.6%
69Richland County15,219−3.7%
70De Witt County15,118−2.1%
71Clark County15,114−2.2%
72Moultrie County14,371−0.8%
73Pike County14,231−2.8%
74Lawrence County13,790−9.7%
75Washington County13,564−1.2%
76Massac County13,502−4.5%
77Johnson County13,363+0.3%
78White County13,250−4.0%
79Ford County13,216−2.2%
80Clay County12,793−3.6%
81Cass County12,463−4.0%
82Mason County12,411−4.9%
83Menard County11,863−3.3%
84Marshall County11,473−2.0%
85Greene County11,313−5.1%
86Wabash County10,907−3.6%
87Cumberland County10,208−2.1%
88Jasper County9,032−2.4%
89Hamilton County7,859−1.7%
90Schuyler County6,657−3.0%
91Brown County6,401+2.7%
92Henderson County5,984−5.6%
93Edwards County5,898−5.0%
94Putnam County5,619−0.1%
95Stark County5,319−1.2%
96Scott County4,866−4.0%
97Pulaski County4,820−6.9%
98Gallatin County4,616−6.4%
99Alexander County4,570−11.6%
100Calhoun County4,300−2.3%
101Pope County3,672−2.2%
102Hardin County3,588−1.8%

How this is ranked

The Census Bureau's July 1 resident population estimates for 2025, largest first, with the change since 2020. Counties with fewer than 1,000 residents are not ranked. Areas without an estimate for the same year as the others are not ranked.

Source: U.S. Census Bureau, Population Estimates Program (Vintage 2025). Figures come from public federal statistics and are informational only, not investment advice. Check the source before relying on a number. Methodology: how ranks and figures are built.

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Questions

What is the largest county in Illinois?

Cook County is the largest county in Illinois, with 5,194,625 residents in 2025 (Census PEP). DuPage County (934,298) and Lake County (719,339) come next.

How is this ranking calculated?

The Census Bureau's July 1 resident population estimates for 2025, largest first, with the change since 2020. Counties with fewer than 1,000 residents are not ranked. Areas without an estimate for the same year as the others are not ranked.

More rankings for Illinois

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