IL · 2026 Census Gazetteer

Illinois counties by area

Official, comparable measurements for 102 counties and county equivalents.

Source fields preservedGEOID · ALAND · AWATER

County equivalents102

Combined land55,513.5 mi²

Combined water2,399.7 mi²

Largest by landMcLean County

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.

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.

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.

Complete area table

Sorted from largest to smallest land area.

#	County / equivalent	Land	Water	Water share
1	McLean CountyGEOID 17113	1,183.2 mi²	3 mi²	0.3%
2	LaSalle CountyGEOID 17099	1,135.1 mi²	13.1 mi²	1.1%
3	Iroquois CountyGEOID 17075	1,117.4 mi²	1.6 mi²	0.1%
4	Livingston CountyGEOID 17105	1,043.6 mi²	2.3 mi²	0.2%
5	Champaign CountyGEOID 17019	996.1 mi²	2.4 mi²	0.2%
6	Cook CountyGEOID 17031	944.9 mi²	689.7 mi²	42.2%
7	Vermilion CountyGEOID 17183	898.3 mi²	2.9 mi²	0.3%
8	Bureau CountyGEOID 17011	869.1 mi²	4.4 mi²	0.5%
9	Sangamon CountyGEOID 17167	868.2 mi²	8.8 mi²	1%
10	Fulton CountyGEOID 17057	865.7 mi²	16.9 mi²	1.9%
11	Macoupin CountyGEOID 17117	863 mi²	4.7 mi²	0.5%
12	Adams CountyGEOID 17001	855.2 mi²	16.1 mi²	1.9%
13	Will CountyGEOID 17197	835.9 mi²	13.3 mi²	1.6%
14	Pike CountyGEOID 17149	831.4 mi²	17.5 mi²	2.1%
15	Henry CountyGEOID 17073	823.2 mi²	2.5 mi²	0.3%
16	Hancock CountyGEOID 17067	793.7 mi²	20.7 mi²	2.5%
17	Ogle CountyGEOID 17141	758.7 mi²	4.8 mi²	0.6%
18	Shelby CountyGEOID 17173	758.5 mi²	9.6 mi²	1.2%
19	Lee CountyGEOID 17103	724.8 mi²	3.8 mi²	0.5%
20	Fayette CountyGEOID 17051	716.5 mi²	8.8 mi²	1.2%
21	Knox CountyGEOID 17095	716.4 mi²	3.4 mi²	0.5%
22	Madison CountyGEOID 17119	715.5 mi²	24.4 mi²	3.3%
23	Wayne CountyGEOID 17191	713.8 mi²	1.6 mi²	0.2%
24	Christian CountyGEOID 17021	709.5 mi²	6.3 mi²	0.9%
25	Montgomery CountyGEOID 17135	703.8 mi²	6 mi²	0.8%
26	Whiteside CountyGEOID 17195	684.1 mi²	12.3 mi²	1.8%
27	Kankakee CountyGEOID 17091	676.5 mi²	4.8 mi²	0.7%
28	St. Clair CountyGEOID 17163	657.7 mi²	16.1 mi²	2.4%
29	Tazewell CountyGEOID 17179	646.5 mi²	11.5 mi²	1.7%
30	DeKalb CountyGEOID 17037	631.3 mi²	3.3 mi²	0.5%
31	Edgar CountyGEOID 17045	623.3 mi²	0.6 mi²	0.1%
32	Peoria CountyGEOID 17143	618.7 mi²	11.6 mi²	1.8%
33	Logan CountyGEOID 17107	618.1 mi²	0.9 mi²	0.1%
34	McHenry CountyGEOID 17111	603.4 mi²	7.7 mi²	1.3%
35	Jo Daviess CountyGEOID 17085	600.9 mi²	17.7 mi²	2.9%
36	McDonough CountyGEOID 17109	589.3 mi²	0.8 mi²	0.1%
37	Jackson CountyGEOID 17077	583.6 mi²	18.7 mi²	3.1%
38	Macon CountyGEOID 17115	580.5 mi²	5.2 mi²	0.9%
39	Randolph CountyGEOID 17157	575.4 mi²	21.7 mi²	3.6%
40	Marion CountyGEOID 17121	572.5 mi²	3.6 mi²	0.6%
41	Jefferson CountyGEOID 17081	571.2 mi²	12.6 mi²	2.2%
42	Morgan CountyGEOID 17137	569 mi²	3.5 mi²	0.6%
43	Stephenson CountyGEOID 17177	564.2 mi²	0.5 mi²	0.1%
44	Washington CountyGEOID 17189	562.6 mi²	1.3 mi²	0.2%
45	Mercer CountyGEOID 17131	561.2 mi²	7.5 mi²	1.3%
46	Greene CountyGEOID 17061	543.1 mi²	3.3 mi²	0.6%
47	Warren CountyGEOID 17187	542.4 mi²	0.7 mi²	0.1%
48	Mason CountyGEOID 17125	539.4 mi²	24.2 mi²	4.3%
49	Woodford CountyGEOID 17203	527.6 mi²	15.4 mi²	2.8%
50	Kane CountyGEOID 17089	519.4 mi²	4.8 mi²	0.9%
51	Winnebago CountyGEOID 17201	513 mi²	6.1 mi²	1.2%
52	Coles CountyGEOID 17029	508.3 mi²	1.8 mi²	0.4%
53	Clark CountyGEOID 17023	501.4 mi²	3.4 mi²	0.7%
54	White CountyGEOID 17193	495 mi²	6.9 mi²	1.4%
55	Jasper CountyGEOID 17079	494.6 mi²	3.6 mi²	0.7%
56	Ford CountyGEOID 17053	485.6 mi²	0.6 mi²	0.1%
57	Effingham CountyGEOID 17049	478.8 mi²	1.2 mi²	0.3%
58	Clinton CountyGEOID 17027	473.9 mi²	29.2 mi²	5.8%
59	Clay CountyGEOID 17025	468.4 mi²	1.2 mi²	0.3%
60	Carroll CountyGEOID 17015	445.4 mi²	21.6 mi²	4.6%
61	Lake CountyGEOID 17097	443.7 mi²	924.7 mi²	67.6%
62	Crawford CountyGEOID 17033	443.6 mi²	2.2 mi²	0.5%
63	Perry CountyGEOID 17145	441.9 mi²	5.1 mi²	1.1%
64	Piatt CountyGEOID 17147	439.2 mi²	0.3 mi²	0.1%
65	Schuyler CountyGEOID 17169	437.3 mi²	4.1 mi²	0.9%
66	Hamilton CountyGEOID 17065	434.7 mi²	1.2 mi²	0.3%
67	Rock Island CountyGEOID 17161	427.5 mi²	23.8 mi²	5.3%
68	Williamson CountyGEOID 17199	420.2 mi²	24.1 mi²	5.4%
69	Grundy CountyGEOID 17063	418.1 mi²	12.4 mi²	2.9%
70	Douglas CountyGEOID 17041	416.7 mi²	0.6 mi²	0.1%
71	Union CountyGEOID 17181	413.4 mi²	8.7 mi²	2.1%
72	Franklin CountyGEOID 17055	408.9 mi²	22.5 mi²	5.2%
73	De Witt CountyGEOID 17039	397.6 mi²	7.5 mi²	1.9%
74	Marshall CountyGEOID 17123	386.8 mi²	11.7 mi²	2.9%
75	Monroe CountyGEOID 17133	385.3 mi²	13 mi²	3.3%
76	Bond CountyGEOID 17005	380.3 mi²	2.5 mi²	0.7%
77	Saline CountyGEOID 17165	380 mi²	6.9 mi²	1.8%
78	Henderson CountyGEOID 17071	378.8 mi²	16.4 mi²	4.2%
79	Cass CountyGEOID 17017	375.8 mi²	7.9 mi²	2.1%
80	Lawrence CountyGEOID 17101	372.2 mi²	2 mi²	0.5%
81	Jersey CountyGEOID 17083	369.6 mi²	7.9 mi²	2.1%
82	Pope CountyGEOID 17151	368.9 mi²	5.7 mi²	1.5%
83	Richland CountyGEOID 17159	360 mi²	1.9 mi²	0.5%
84	Cumberland CountyGEOID 17035	345.9 mi²	1 mi²	0.3%
85	Johnson CountyGEOID 17087	343.7 mi²	4.9 mi²	1.4%
86	Moultrie CountyGEOID 17139	336 mi²	8.5 mi²	2.5%
87	DuPage CountyGEOID 17043	327.9 mi²	8.5 mi²	2.5%
88	Gallatin CountyGEOID 17059	322.9 mi²	5.2 mi²	1.6%
89	Kendall CountyGEOID 17093	320.2 mi²	2 mi²	0.6%
90	Menard CountyGEOID 17129	314.4 mi²	1 mi²	0.3%
91	Brown CountyGEOID 17009	305.7 mi²	1.6 mi²	0.5%
92	Stark CountyGEOID 17175	288.1 mi²	0.3 mi²	0.1%
93	Boone CountyGEOID 17007	280.7 mi²	1.3 mi²	0.5%
94	Calhoun CountyGEOID 17013	253.8 mi²	29.8 mi²	10.5%
95	Scott CountyGEOID 17171	250.8 mi²	1.9 mi²	0.7%
96	Massac CountyGEOID 17127	237.2 mi²	4.9 mi²	2%
97	Alexander CountyGEOID 17003	235.4 mi²	17.2 mi²	6.8%
98	Wabash CountyGEOID 17185	223.3 mi²	4.2 mi²	1.9%
99	Edwards CountyGEOID 17047	222.4 mi²	0.3 mi²	0.1%
100	Pulaski CountyGEOID 17153	199.3 mi²	3.8 mi²	1.9%
101	Hardin CountyGEOID 17069	177.4 mi²	4 mi²	2.2%
102	Putnam CountyGEOID 17155	160.1 mi²	12 mi²	7%

How to read this table. Land and water areas are Census statistical measurements in square miles. Adding county rows can differ slightly from separately published state totals because of rounding and geographic treatment.