Rank |
County |
Population (2012) |
1 |
Cook County, Illinois
|
5,231,351
|
2 |
DuPage County, Illinois
|
927,987
|
3 |
Lake County, Illinois
|
702,120
|
4 |
Will County, Illinois
|
682,518
|
5 |
Kane County, Illinois
|
522,487
|
6 |
McHenry County, Illinois
|
308,145
|
7 |
Winnebago County, Illinois
|
292,069
|
8 |
St Clair County, Illinois
|
268,858
|
9 |
Madison County, Illinois
|
267,883
|
10 |
Champaign County, Illinois
|
203,276
|
11 |
Sangamon County, Illinois
|
199,271
|
12 |
Peoria County, Illinois
|
187,254
|
13 |
McLean County, Illinois
|
172,281
|
14 |
Rock Island County, Illinois
|
147,457
|
15 |
Tazewell County, Illinois
|
135,949
|
16 |
Kendall County, Illinois
|
118,105
|
17 |
Kankakee County, Illinois
|
113,040
|
18 |
LaSalle County, Illinois
|
112,973
|
19 |
Macon County, Illinois
|
110,122
|
20 |
DeKalb County, Illinois
|
104,704
|
21 |
Vermilion County, Illinois
|
80,727
|
22 |
Adams County, Illinois
|
67,197
|
23 |
Williamson County, Illinois
|
66,674
|
24 |
Jackson County, Illinois
|
60,071
|
25 |
Whiteside County, Illinois
|
57,846
|
26 |
Boone County, Illinois
|
53,940
|
27 |
Coles County, Illinois
|
53,655
|
28 |
Ogle County, Illinois
|
52,848
|
29 |
Knox County, Illinois
|
52,247
|
30 |
Grundy County, Illinois
|
50,281
|
31 |
Henry County, Illinois
|
50,155
|
32 |
Macoupin County, Illinois
|
47,231
|
33 |
Stephenson County, Illinois
|
46,959
|
34 |
Franklin County, Illinois
|
39,407
|
35 |
Woodford County, Illinois
|
38,971
|
36 |
Marion County, Illinois
|
38,894
|
37 |
Jefferson County, Illinois
|
38,720
|
38 |
Livingston County, Illinois
|
38,647
|
39 |
Clinton County, Illinois
|
38,061
|
40 |
Fulton County, Illinois
|
36,651
|
41 |
Morgan County, Illinois
|
35,272
|
42 |
Lee County, Illinois
|
35,037
|
43 |
Christian County, Illinois
|
34,638
|
44 |
Effingham County, Illinois
|
34,353
|
45 |
Bureau County, Illinois
|
34,323
|
46 |
Monroe County, Illinois
|
33,357
|
47 |
Randolph County, Illinois
|
32,956
|
48 |
McDonough County, Illinois
|
32,537
|
49 |
Logan County, Illinois
|
30,013
|
50 |
Montgomery County, Illinois
|
29,620
|
51 |
Iroquois County, Illinois
|
29,240
|
52 |
Saline County, Illinois
|
24,946
|
53 |
Jersey County, Illinois
|
22,742
|
54 |
Jo Daviess County, Illinois
|
22,549
|
55 |
Shelby County, Illinois
|
22,196
|
56 |
Perry County, Illinois
|
22,058
|
57 |
Fayette County, Illinois
|
22,014
|
58 |
Douglas County, Illinois
|
19,853
|
59 |
Crawford County, Illinois
|
19,600
|
60 |
Hancock County, Illinois
|
18,891
|
61 |
Edgar County, Illinois
|
18,191
|
62 |
Warren County, Illinois
|
17,731
|
63 |
Union County, Illinois
|
17,647
|
64 |
Bond County, Illinois
|
17,644
|
65 |
Lawrence County, Illinois
|
16,604
|
66 |
Wayne County, Illinois
|
16,574
|
67 |
Piatt County, Illinois
|
16,504
|
68 |
De Witt County, Illinois
|
16,434
|
69 |
Pike County, Illinois
|
16,308
|
70 |
Mercer County, Illinois
|
16,219
|
71 |
Clark County, Illinois
|
16,209
|
72 |
Richland County, Illinois
|
16,176
|
73 |
Massac County, Illinois
|
15,234
|
74 |
Carroll County, Illinois
|
15,011
|
75 |
Moultrie County, Illinois
|
14,933
|
76 |
Washington County, Illinois
|
14,598
|
77 |
White County, Illinois
|
14,568
|
78 |
Mason County, Illinois
|
14,327
|
79 |
Ford County, Illinois
|
14,008
|
80 |
Clay County, Illinois
|
13,766
|
81 |
Greene County, Illinois
|
13,576
|
82 |
Cass County, Illinois
|
13,338
|
83 |
Johnson County, Illinois
|
12,760
|
84 |
Menard County, Illinois
|
12,722
|
85 |
Marshall County, Illinois
|
12,327
|
86 |
Wabash County, Illinois
|
11,727
|
87 |
Cumberland County, Illinois
|
10,968
|
88 |
Jasper County, Illinois
|
9,614
|
89 |
Hamilton County, Illinois
|
8,370
|
90 |
Alexander County, Illinois
|
7,748
|
91 |
Schuyler County, Illinois
|
7,457
|
92 |
Henderson County, Illinois
|
7,043
|
93 |
Brown County, Illinois
|
6,914
|
94 |
Edwards County, Illinois
|
6,684
|
95 |
Pulaski County, Illinois
|
5,998
|
96 |
Stark County, Illinois
|
5,946
|
97 |
Putnam County, Illinois
|
5,886
|
98 |
Gallatin County, Illinois
|
5,430
|
99 |
Scott County, Illinois
|
5,290
|
100 |
Calhoun County, Illinois
|
5,014
|
101 |
Pope County, Illinois
|
4,272
|
102 |
Hardin County, Illinois
|
4,258
|