County facts · Land area · October 21, 2026
Largest Counties in Illinois by Area and Population
The largest Illinois counties by land area and by 2023 population, plus the smallest, county seats and a link to each official parcel map.
Looking for the largest counties in Illinois? Illinois has 102 counties covering about 55,513 square miles of land, based on the Census Bureau's 2020 Gazetteer. The largest by land area is McLean County, at about 1,183 square miles, roughly 7.4 times the size of the smallest, Putnam County (160 sq mi). Measured by people instead, the largest is Cook County, with about 5,087,072 residents in the Census Bureau's July 1, 2023 estimate.
Each table below links the county's Platbookmapper page and its official parcel viewer, so you can go straight from the numbers to the property lines.
Illinois counties at a glance
- Counties: 102
- Land area: about 55,513 sq mi, plus about 2,400 sq mi of water inside county lines
- Residents, 2023 estimates: about 12,549,689, or about 226 people per square mile of land
- Median county land area: about 511 sq mi
- With a verified public parcel viewer in our directory: 97 of 102
The 10 largest Illinois counties by land area
| # | County | Seat | Land (sq mi) | 2023 pop. | People per sq mi | Parcel viewer |
|---|---|---|---|---|---|---|
| 1 | McLean County | Bloomington | 1,183 | 170,441 | 144 | ArcGIS Experience Builder |
| 2 | LaSalle County | Ottawa | 1,135 | 108,309 | 95 | county web map |
| 3 | Iroquois County | Watseka | 1,117 | 26,136 | 23 | BHA Maps |
| 4 | Livingston County | Pontiac | 1,044 | 35,320 | 34 | CAMAvision Maps |
| 5 | Champaign County | Urbana | 996 | 205,644 | 206 | county web map |
| 6 | Cook County | Chicago | 945 | 5,087,072 | 5,384 | county web map |
| 7 | Vermilion County | Danville | 898 | 71,652 | 80 | BHA Maps |
| 8 | Bureau County | Princeton | 869 | 32,729 | 38 | ArcGIS Experience Builder |
| 9 | Sangamon County | Springfield | 868 | 193,491 | 223 | county web map |
| 10 | Fulton County | Lewistown | 866 | 32,541 | 38 | ArcGIS Web AppBuilder |
Together these 10 cover about 18% of Illinois's land area and hold about 48% of its residents.
The 10 most populous Illinois counties
| # | County | Seat | 2023 pop. | Land (sq mi) | Parcel viewer |
|---|---|---|---|---|---|
| 1 | Cook County | Chicago | 5,087,072 | 945 | county web map |
| 2 | DuPage County | Wheaton | 921,213 | 328 | county web map |
| 3 | Lake County | Waukegan | 708,760 | 444 | county web map |
| 4 | Will County | Joliet | 700,728 | 836 | county web map |
| 5 | Kane County | Geneva | 514,982 | 519 | county web map |
| 6 | McHenry County | Woodstock | 312,800 | 603 | county web map |
| 7 | Winnebago County | Rockford | 280,922 | 513 | county web map |
| 8 | Madison County | Edwardsville | 262,752 | 716 | county web map |
| 9 | St. Clair County | Belleville | 251,018 | 658 | county web map |
| 10 | Champaign County | Urbana | 205,644 | 996 | county web map |
These 10 hold about 74% of Illinois's residents in the 2023 estimates.
The 5 smallest Illinois counties by land area
| County | Seat | Land (sq mi) | 2023 pop. | Parcel viewer |
|---|---|---|---|---|
| Putnam County | Hennepin | 160 | 5,561 | WTH GIS |
| Hardin County | Elizabethtown | 177 | 3,569 | no verified public viewer listed yet |
| Pulaski County | Mound City | 199 | 4,911 | ArcGIS Web AppBuilder |
| Edwards County | Albion | 222 | 5,968 | BHA Maps |
| Wabash County | Mount Carmel | 223 | 10,942 | BHA Maps |
Most and least crowded
- Most people per square mile: Cook County, about 5,384 (then DuPage County, 2,810, and Lake County, 1,598)
- Fewest people per square mile: Pope County, about 10 (then Gallatin County, 14, and Schuyler County, 15)
Counties with the most water
The Census Bureau reports water separately from land. It counts lakes, reservoirs, rivers and, for coastal and Great Lakes counties, the water inside the county boundary.
- Lake County: about 925 sq mi of water, 68% of its total area
- Cook County: about 690 sq mi of water, 42% of its total area
- Calhoun County: about 30 sq mi of water, 10% of its total area
Using these numbers in a land search
- Land area is not parcel count. A large rural county can hold fewer parcels than a small suburban one, so size alone says little about how busy its parcel map is.
- Search, don't scroll. In a big county, type an address, owner name or parcel number into the viewer's search box, where it has one, instead of panning across the map.
- Records follow the county line. Deeds, plats and tax bills are kept by the county where the parcel sits, so a tract that crosses a county line usually has a parcel number in each county.
- Rounded figures. Land and water areas are rounded to whole square miles. People per square mile is the 2023 estimate divided by land area.
Related guides
- Illinois county GIS websites by viewer
- Illinois landowner maps for hunting
- Illinois–Indiana border counties
- Illinois–Iowa border counties
- Illinois–Kentucky border counties
- Illinois–Missouri border counties
- Illinois–Wisconsin border counties
More: All Illinois counties on Platbookmapper
Sources
- U.S. Census Bureau Gazetteer files, 2020 county land and water area.
- U.S. Census Bureau, Population Estimates Program, county totals, Vintage 2023 (July 1, 2023 estimates)
- Platbookmapper county GIS directory (live data file behind our county pages, pulled October 21, 2026) for each county's official parcel viewer.
- County seats: Wikidata (county seat property), cross-checked against Census place names.