Illinois County Area & Size Rankings

Understanding Illinois’s county areas

The land-area range runs from Putnam County at 160.1 mi² to McLean County at 1,183.2 mi². The largest has 7.4 times the land area of the smallest and accounts for 2.1% of the combined county land in Illinois. Compare with every state’s largest county.

The median county-equivalent land area is 510.7 mi², below the national median of 604.5 mi². The median describes the middle of the county size distribution; it does not describe how people or development are distributed. A state with a few very large counties can have a much smaller median than its largest entry suggests.

Where water changes the picture

Lake County has the most assigned water area, at 924.7 mi². It also has the highest water share, with water making up 67.6% of its total area. Water area and water percentage answer different questions: the first measures an amount, while the second measures the mix of land and water.

Across all 102 entries, water accounts for 4.1% of the combined total area. This is calculated from the summed land and water measurements, rather than averaging county percentages, which would give each small and large county equal weight.

Where people live

An estimated 12,719,141 people lived in Illinois on July 1, 2025 (−0.8% since 2020), or 3.7% of the national total in this dataset. Cook County is the most populous county equivalent, with 5,194,625 residents — 40.8% of the state. The largest by land, McLean County, has 171,419.

Across the state there are 229 people per square mile of land. County densities range from 5,497 in Cook County to 10 in Pope County; the median county equivalent has 44. Switch the map above to density to see where the state’s population concentrates.

Compare the largest and smallest county equivalents in Illinois to see land, water, and total area on the same scale.

These calculations use the 2026 Census county records listed below. County-equivalent boundaries vary between states; area alone does not measure population, density, or usable land. See coverage and calculation rules.

#	County / equivalent	Land	Water	Water share	Population	Per mi²
1	McLean CountyGEOID 17113	1,183.2 mi²	3 mi²	0.3%	171,419	145
2	LaSalle CountyGEOID 17099	1,135.1 mi²	13.1 mi²	1.1%	107,773	95
3	Iroquois CountyGEOID 17075	1,117.4 mi²	1.6 mi²	0.1%	26,150	23
4	Livingston CountyGEOID 17105	1,043.6 mi²	2.3 mi²	0.2%	35,057	34
5	Champaign CountyGEOID 17019	996.1 mi²	2.4 mi²	0.2%	209,972	211
6	Cook CountyGEOID 17031	944.9 mi²	689.7 mi²	42.2%	5,194,625	5,497
7	Vermilion CountyGEOID 17183	898.3 mi²	2.9 mi²	0.3%	71,259	79
8	Bureau CountyGEOID 17011	869.1 mi²	4.4 mi²	0.5%	32,510	37
9	Sangamon CountyGEOID 17167	868.2 mi²	8.8 mi²	1%	194,170	224
10	Fulton CountyGEOID 17057	865.7 mi²	16.9 mi²	1.9%	32,901	38
11	Macoupin CountyGEOID 17117	863 mi²	4.7 mi²	0.5%	43,748	51
12	Adams CountyGEOID 17001	855.2 mi²	16.1 mi²	1.9%	64,267	75
13	Will CountyGEOID 17197	835.9 mi²	13.3 mi²	1.6%	712,253	852
14	Pike CountyGEOID 17149	831.4 mi²	17.5 mi²	2.1%	14,231	17
15	Henry CountyGEOID 17073	823.2 mi²	2.5 mi²	0.3%	48,095	58
16	Hancock CountyGEOID 17067	793.7 mi²	20.7 mi²	2.5%	16,803	21
17	Ogle CountyGEOID 17141	758.7 mi²	4.8 mi²	0.6%	51,399	68
18	Shelby CountyGEOID 17173	758.5 mi²	9.6 mi²	1.2%	20,576	27
19	Lee CountyGEOID 17103	724.8 mi²	3.8 mi²	0.5%	32,914	45
20	Fayette CountyGEOID 17051	716.5 mi²	8.8 mi²	1.2%	20,790	29
21	Knox CountyGEOID 17095	716.4 mi²	3.4 mi²	0.5%	47,767	67
22	Madison CountyGEOID 17119	715.5 mi²	24.4 mi²	3.3%	263,110	368
23	Wayne CountyGEOID 17191	713.8 mi²	1.6 mi²	0.2%	15,882	22
24	Christian CountyGEOID 17021	709.5 mi²	6.3 mi²	0.9%	33,443	47
25	Montgomery CountyGEOID 17135	703.8 mi²	6 mi²	0.8%	28,076	40
26	Whiteside CountyGEOID 17195	684.1 mi²	12.3 mi²	1.8%	54,121	79
27	Kankakee CountyGEOID 17091	676.5 mi²	4.8 mi²	0.7%	105,525	156
28	St. Clair CountyGEOID 17163	657.7 mi²	16.1 mi²	2.4%	250,708	381
29	Tazewell CountyGEOID 17179	646.5 mi²	11.5 mi²	1.7%	130,049	201
30	DeKalb CountyGEOID 17037	631.3 mi²	3.3 mi²	0.5%	101,835	161
31	Edgar CountyGEOID 17045	623.3 mi²	0.6 mi²	0.1%	16,323	26
32	Peoria CountyGEOID 17143	618.7 mi²	11.6 mi²	1.8%	178,553	289
33	Logan CountyGEOID 17107	618.1 mi²	0.9 mi²	0.1%	27,182	44
34	McHenry CountyGEOID 17111	603.4 mi²	7.7 mi²	1.3%	317,751	527
35	Jo Daviess CountyGEOID 17085	600.9 mi²	17.7 mi²	2.9%	21,594	36
36	McDonough CountyGEOID 17109	589.3 mi²	0.8 mi²	0.1%	25,916	44
37	Jackson CountyGEOID 17077	583.6 mi²	18.7 mi²	3.1%	52,501	90
38	Macon CountyGEOID 17115	580.5 mi²	5.2 mi²	0.9%	99,300	171
39	Randolph CountyGEOID 17157	575.4 mi²	21.7 mi²	3.6%	29,921	52
40	Marion CountyGEOID 17121	572.5 mi²	3.6 mi²	0.6%	36,382	64
41	Jefferson CountyGEOID 17081	571.2 mi²	12.6 mi²	2.2%	36,147	63
42	Morgan CountyGEOID 17137	569 mi²	3.5 mi²	0.6%	32,515	57
43	Stephenson CountyGEOID 17177	564.2 mi²	0.5 mi²	0.1%	43,220	77
44	Washington CountyGEOID 17189	562.6 mi²	1.3 mi²	0.2%	13,564	24
45	Mercer CountyGEOID 17131	561.2 mi²	7.5 mi²	1.3%	15,229	27
46	Greene CountyGEOID 17061	543.1 mi²	3.3 mi²	0.6%	11,313	21
47	Warren CountyGEOID 17187	542.4 mi²	0.7 mi²	0.1%	16,222	30
48	Mason CountyGEOID 17125	539.4 mi²	24.2 mi²	4.3%	12,411	23
49	Woodford CountyGEOID 17203	527.6 mi²	15.4 mi²	2.8%	38,111	72
50	Kane CountyGEOID 17089	519.4 mi²	4.8 mi²	0.9%	525,757	1,012
51	Winnebago CountyGEOID 17201	513 mi²	6.1 mi²	1.2%	283,674	553
52	Coles CountyGEOID 17029	508.3 mi²	1.8 mi²	0.4%	46,607	92
53	Clark CountyGEOID 17023	501.4 mi²	3.4 mi²	0.7%	15,114	30
54	White CountyGEOID 17193	495 mi²	6.9 mi²	1.4%	13,250	27
55	Jasper CountyGEOID 17079	494.6 mi²	3.6 mi²	0.7%	9,032	18
56	Ford CountyGEOID 17053	485.6 mi²	0.6 mi²	0.1%	13,216	27
57	Effingham CountyGEOID 17049	478.8 mi²	1.2 mi²	0.3%	34,519	72
58	Clinton CountyGEOID 17027	473.9 mi²	29.2 mi²	5.8%	37,128	78
59	Clay CountyGEOID 17025	468.4 mi²	1.2 mi²	0.3%	12,793	27
60	Carroll CountyGEOID 17015	445.4 mi²	21.6 mi²	4.6%	15,419	35
61	Lake CountyGEOID 17097	443.7 mi²	924.7 mi²	67.6%	719,339	1,621
62	Crawford CountyGEOID 17033	443.6 mi²	2.2 mi²	0.5%	18,648	42
63	Perry CountyGEOID 17145	441.9 mi²	5.1 mi²	1.1%	20,160	46
64	Piatt CountyGEOID 17147	439.2 mi²	0.3 mi²	0.1%	16,791	38
65	Schuyler CountyGEOID 17169	437.3 mi²	4.1 mi²	0.9%	6,657	15
66	Hamilton CountyGEOID 17065	434.7 mi²	1.2 mi²	0.3%	7,859	18
67	Rock Island CountyGEOID 17161	427.5 mi²	23.8 mi²	5.3%	141,869	332
68	Williamson CountyGEOID 17199	420.2 mi²	24.1 mi²	5.4%	67,225	160
69	Grundy CountyGEOID 17063	418.1 mi²	12.4 mi²	2.9%	54,052	129
70	Douglas CountyGEOID 17041	416.7 mi²	0.6 mi²	0.1%	19,880	48
71	Union CountyGEOID 17181	413.4 mi²	8.7 mi²	2.1%	16,656	40
72	Franklin CountyGEOID 17055	408.9 mi²	22.5 mi²	5.2%	36,916	90
73	De Witt CountyGEOID 17039	397.6 mi²	7.5 mi²	1.9%	15,118	38
74	Marshall CountyGEOID 17123	386.8 mi²	11.7 mi²	2.9%	11,473	30
75	Monroe CountyGEOID 17133	385.3 mi²	13 mi²	3.3%	34,840	90
76	Bond CountyGEOID 17005	380.3 mi²	2.5 mi²	0.7%	16,959	45
77	Saline CountyGEOID 17165	380 mi²	6.9 mi²	1.8%	22,772	60
78	Henderson CountyGEOID 17071	378.8 mi²	16.4 mi²	4.2%	5,984	16
79	Cass CountyGEOID 17017	375.8 mi²	7.9 mi²	2.1%	12,463	33
80	Lawrence CountyGEOID 17101	372.2 mi²	2 mi²	0.5%	13,790	37
81	Jersey CountyGEOID 17083	369.6 mi²	7.9 mi²	2.1%	21,160	57
82	Pope CountyGEOID 17151	368.9 mi²	5.7 mi²	1.5%	3,672	10
83	Richland CountyGEOID 17159	360 mi²	1.9 mi²	0.5%	15,219	42
84	Cumberland CountyGEOID 17035	345.9 mi²	1 mi²	0.3%	10,208	30
85	Johnson CountyGEOID 17087	343.7 mi²	4.9 mi²	1.4%	13,363	39
86	Moultrie CountyGEOID 17139	336 mi²	8.5 mi²	2.5%	14,371	43
87	DuPage CountyGEOID 17043	327.9 mi²	8.5 mi²	2.5%	934,298	2,849
88	Gallatin CountyGEOID 17059	322.9 mi²	5.2 mi²	1.6%	4,616	14
89	Kendall CountyGEOID 17093	320.2 mi²	2 mi²	0.6%	145,470	454
90	Menard CountyGEOID 17129	314.4 mi²	1 mi²	0.3%	11,863	38
91	Brown CountyGEOID 17009	305.7 mi²	1.6 mi²	0.5%	6,401	21
92	Stark CountyGEOID 17175	288.1 mi²	0.3 mi²	0.1%	5,319	18
93	Boone CountyGEOID 17007	280.7 mi²	1.3 mi²	0.5%	53,568	191
94	Calhoun CountyGEOID 17013	253.8 mi²	29.8 mi²	10.5%	4,300	17
95	Scott CountyGEOID 17171	250.8 mi²	1.9 mi²	0.7%	4,866	19
96	Massac CountyGEOID 17127	237.2 mi²	4.9 mi²	2%	13,502	57
97	Alexander CountyGEOID 17003	235.4 mi²	17.2 mi²	6.8%	4,570	19
98	Wabash CountyGEOID 17185	223.3 mi²	4.2 mi²	1.9%	10,907	49
99	Edwards CountyGEOID 17047	222.4 mi²	0.3 mi²	0.1%	5,898	27
100	Pulaski CountyGEOID 17153	199.3 mi²	3.8 mi²	1.9%	4,820	24
101	Hardin CountyGEOID 17069	177.4 mi²	4 mi²	2.2%	3,588	20
102	Putnam CountyGEOID 17155	160.1 mi²	12 mi²	7%	5,619	35

County / equivalent

Land

Water

Water share

Population

Per mi²

McLean CountyGEOID 17113

1,183.2 mi²

3 mi²

0.3%

171,419

145

LaSalle CountyGEOID 17099

1,135.1 mi²

13.1 mi²

1.1%

107,773

Iroquois CountyGEOID 17075

1,117.4 mi²

1.6 mi²

0.1%

26,150

Livingston CountyGEOID 17105

1,043.6 mi²

2.3 mi²

0.2%

35,057

Champaign CountyGEOID 17019

996.1 mi²

2.4 mi²

0.2%

209,972

211

Cook CountyGEOID 17031

944.9 mi²

689.7 mi²

42.2%

5,194,625

5,497

Vermilion CountyGEOID 17183

898.3 mi²

2.9 mi²

0.3%

71,259

Bureau CountyGEOID 17011

869.1 mi²

4.4 mi²

0.5%

32,510

Sangamon CountyGEOID 17167

868.2 mi²

8.8 mi²

194,170

224

Fulton CountyGEOID 17057

865.7 mi²

16.9 mi²

1.9%

32,901

Macoupin CountyGEOID 17117

863 mi²

4.7 mi²

0.5%

43,748

Adams CountyGEOID 17001

855.2 mi²

16.1 mi²

1.9%

64,267

Will CountyGEOID 17197

835.9 mi²

13.3 mi²

1.6%

712,253

852

Pike CountyGEOID 17149

831.4 mi²

17.5 mi²

2.1%

14,231

Henry CountyGEOID 17073

823.2 mi²

2.5 mi²

0.3%

48,095

Hancock CountyGEOID 17067

793.7 mi²

20.7 mi²

2.5%

16,803

Ogle CountyGEOID 17141

758.7 mi²

4.8 mi²

0.6%

51,399

Shelby CountyGEOID 17173

758.5 mi²

9.6 mi²

1.2%

20,576

Lee CountyGEOID 17103

724.8 mi²

3.8 mi²

0.5%

32,914

Fayette CountyGEOID 17051

716.5 mi²

8.8 mi²

1.2%

20,790

Knox CountyGEOID 17095

716.4 mi²

3.4 mi²

0.5%

47,767

Madison CountyGEOID 17119

715.5 mi²

24.4 mi²

3.3%

263,110

368

Wayne CountyGEOID 17191

713.8 mi²

1.6 mi²

0.2%

15,882

Christian CountyGEOID 17021

709.5 mi²

6.3 mi²

0.9%

33,443

Montgomery CountyGEOID 17135

703.8 mi²

6 mi²

0.8%

28,076

Whiteside CountyGEOID 17195

684.1 mi²

12.3 mi²

1.8%

54,121

Kankakee CountyGEOID 17091

676.5 mi²

4.8 mi²

0.7%

105,525

156

St. Clair CountyGEOID 17163

657.7 mi²

16.1 mi²

2.4%

250,708

381

Tazewell CountyGEOID 17179

646.5 mi²

11.5 mi²

1.7%

130,049

201

DeKalb CountyGEOID 17037

631.3 mi²

3.3 mi²

0.5%

101,835

161

Edgar CountyGEOID 17045

623.3 mi²

0.6 mi²

0.1%

16,323

Peoria CountyGEOID 17143

618.7 mi²

11.6 mi²

1.8%

178,553

289

Logan CountyGEOID 17107

618.1 mi²

0.9 mi²

0.1%

27,182

McHenry CountyGEOID 17111

603.4 mi²

7.7 mi²

1.3%

317,751

527

Jo Daviess CountyGEOID 17085

600.9 mi²

17.7 mi²

2.9%

21,594

McDonough CountyGEOID 17109

589.3 mi²

0.8 mi²

0.1%

25,916

Jackson CountyGEOID 17077

583.6 mi²

18.7 mi²

3.1%

52,501

Macon CountyGEOID 17115

580.5 mi²

5.2 mi²

0.9%

99,300

171

Randolph CountyGEOID 17157

575.4 mi²

21.7 mi²

3.6%

29,921

Marion CountyGEOID 17121

572.5 mi²

3.6 mi²

0.6%

36,382

Jefferson CountyGEOID 17081

571.2 mi²

12.6 mi²

2.2%

36,147

Morgan CountyGEOID 17137

569 mi²

3.5 mi²

0.6%

32,515

Stephenson CountyGEOID 17177

564.2 mi²

0.5 mi²

0.1%

43,220

Washington CountyGEOID 17189

562.6 mi²

1.3 mi²

0.2%

13,564

Mercer CountyGEOID 17131

561.2 mi²

7.5 mi²

1.3%

15,229

Greene CountyGEOID 17061

543.1 mi²

3.3 mi²

0.6%

11,313

Warren CountyGEOID 17187

542.4 mi²

0.7 mi²

0.1%

16,222

Mason CountyGEOID 17125

539.4 mi²

24.2 mi²

4.3%

12,411

Woodford CountyGEOID 17203

527.6 mi²

15.4 mi²

2.8%

38,111

Kane CountyGEOID 17089

519.4 mi²

4.8 mi²

0.9%

525,757

1,012

Winnebago CountyGEOID 17201

513 mi²

6.1 mi²

1.2%

283,674

553

Coles CountyGEOID 17029

508.3 mi²

1.8 mi²

0.4%

46,607

Clark CountyGEOID 17023

501.4 mi²

3.4 mi²

0.7%

15,114

White CountyGEOID 17193

495 mi²

6.9 mi²

1.4%

13,250

Jasper CountyGEOID 17079

494.6 mi²

3.6 mi²

0.7%

9,032

Ford CountyGEOID 17053

485.6 mi²

0.6 mi²

0.1%

13,216

Effingham CountyGEOID 17049

478.8 mi²

1.2 mi²

0.3%

34,519

Clinton CountyGEOID 17027

473.9 mi²

29.2 mi²

5.8%

37,128

Clay CountyGEOID 17025

468.4 mi²

1.2 mi²

0.3%

12,793

Carroll CountyGEOID 17015

445.4 mi²

21.6 mi²

4.6%

15,419

Lake CountyGEOID 17097

443.7 mi²

924.7 mi²

67.6%

719,339

1,621

Crawford CountyGEOID 17033

443.6 mi²

2.2 mi²

0.5%

18,648

Perry CountyGEOID 17145

441.9 mi²

5.1 mi²

1.1%

20,160

Piatt CountyGEOID 17147

439.2 mi²

0.3 mi²

0.1%

16,791

Schuyler CountyGEOID 17169

437.3 mi²

4.1 mi²

0.9%

6,657

Hamilton CountyGEOID 17065

434.7 mi²

1.2 mi²

0.3%

7,859

Rock Island CountyGEOID 17161

427.5 mi²

23.8 mi²

5.3%

141,869

332

Williamson CountyGEOID 17199

420.2 mi²

24.1 mi²

5.4%

67,225

160

Grundy CountyGEOID 17063

418.1 mi²

12.4 mi²

2.9%

54,052

129

Douglas CountyGEOID 17041

416.7 mi²

0.6 mi²

0.1%

19,880

Union CountyGEOID 17181

413.4 mi²

8.7 mi²

2.1%

16,656

Franklin CountyGEOID 17055

408.9 mi²

22.5 mi²

5.2%

36,916

De Witt CountyGEOID 17039

397.6 mi²

7.5 mi²

1.9%

15,118

Marshall CountyGEOID 17123

386.8 mi²

11.7 mi²

2.9%

11,473

Monroe CountyGEOID 17133

385.3 mi²

13 mi²

3.3%

34,840

Bond CountyGEOID 17005

380.3 mi²

2.5 mi²

0.7%

16,959

Saline CountyGEOID 17165

380 mi²

6.9 mi²

1.8%

22,772

Henderson CountyGEOID 17071

378.8 mi²

16.4 mi²

4.2%

5,984

Cass CountyGEOID 17017

375.8 mi²

7.9 mi²

2.1%

12,463

Lawrence CountyGEOID 17101

372.2 mi²

2 mi²

0.5%

13,790

Jersey CountyGEOID 17083

369.6 mi²

7.9 mi²

2.1%

21,160

Pope CountyGEOID 17151

368.9 mi²

5.7 mi²

1.5%

3,672

Richland CountyGEOID 17159

360 mi²

1.9 mi²

0.5%

15,219

Cumberland CountyGEOID 17035

345.9 mi²

1 mi²

0.3%

10,208

Johnson CountyGEOID 17087

343.7 mi²

4.9 mi²

1.4%

13,363

Moultrie CountyGEOID 17139

336 mi²

8.5 mi²

2.5%

14,371

DuPage CountyGEOID 17043

327.9 mi²

8.5 mi²

2.5%

934,298

2,849

Gallatin CountyGEOID 17059

322.9 mi²

5.2 mi²

1.6%

4,616

Kendall CountyGEOID 17093

320.2 mi²

2 mi²

0.6%

145,470

454

Menard CountyGEOID 17129

314.4 mi²

1 mi²

0.3%

11,863

Brown CountyGEOID 17009

305.7 mi²

1.6 mi²

0.5%

6,401

Stark CountyGEOID 17175

288.1 mi²

0.3 mi²

0.1%

5,319

Boone CountyGEOID 17007

280.7 mi²

1.3 mi²

0.5%

53,568

191

Calhoun CountyGEOID 17013

253.8 mi²

29.8 mi²

10.5%

4,300

Scott CountyGEOID 17171

250.8 mi²

1.9 mi²

0.7%

4,866

Massac CountyGEOID 17127

237.2 mi²

4.9 mi²

13,502

Alexander CountyGEOID 17003

235.4 mi²

17.2 mi²

6.8%

4,570

Wabash CountyGEOID 17185

223.3 mi²

4.2 mi²

1.9%

10,907

Edwards CountyGEOID 17047

222.4 mi²

0.3 mi²

0.1%

5,898

100

Pulaski CountyGEOID 17153

199.3 mi²

3.8 mi²

1.9%

4,820

101

Hardin CountyGEOID 17069

177.4 mi²

4 mi²

2.2%

3,588

102

Putnam CountyGEOID 17155

160.1 mi²

12 mi²

5,619

Illinois counties by area

Understanding Illinois’s county areas

Where water changes the picture

Where people live

Complete area table