County Maps US

Cook County, Illinois

The most populous of Illinois's 102 counties.

CountyFIPS 17031

Within Illinois
Cook County, highlighted, with the areas around it. Boundaries generalised from the 2025 Census cartographic boundary file; neighbour fills carry no data. The dot marks Chicago, the county seat, located via the 2025 Census Gazetteer.

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Population
5,194,625
-69,026 (-1.3%) since 2020
Land area
944.9
square miles. A further 42.2% of the total area is water
Population density
5,497
people per square mile, computed rather than published
County seat
Chicago
Seat of county government.
Established
1831
194 years ago
Largest city
Chicago city
Population 2,731,585 for the whole place, which extends beyond this county.

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.

Satellite view

Aerial imagery of Cook County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.

Aerial view of Cook County, Illinois from the USGS National Map, with its boundary outlined
Imagery: USGS National Map, USGS Imagery Only, public domain, requested from USGS by your browser when you reach this point on the page, at 661 by 800 pixels. The boundary is the 2025 Census cartographic boundary file, reprojected to Web Mercator to match the imagery. You can also open the USGS National Map viewer.

Where Cook County ranks

Position among the 102 counties of Illinois, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn IllinoisNationally
Population5,194,6251st of 1022nd of 3,144
Land area944.9 sq mi6th of 102751st of 3,144
Population density5,497 per sq mi1st of 10217th of 3,144
Median household income$83,49814th of 102467th of 3,143

Full data for Cook County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population5,194,625Vintage 2025 Population Estimates
Population in 20205,263,651Vintage 2025 Population Estimates
2020 estimates base?5,279,010Vintage 2025 Population Estimates
Land area944.9 sq mi2025 Gazetteer Files
Water area689.7 sq mi2025 Gazetteer Files
Total area1,635 sq mi2025 Gazetteer Files
Population density?5,497 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$83,498American Community Survey 2020-2024 5-Year Estimates
Median home value$324,500American Community Survey 2020-2024 5-Year Estimates
Median age38.0American Community Survey 2020-2024 5-Year Estimates
Households2,100,230American Community Survey 2020-2024 5-Year Estimates
Housing units2,276,493American Community Survey 2020-2024 5-Year Estimates

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.

How the population changed

The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:

Births minus deaths
+9,144
50,997 births, 41,853 deaths
Net migration
-3,554
More people moved out than moved in.

Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.

The 8 areas bordering Cook County

Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.

Bordering areaStateShared borderPopulation
Lake CountyIllinois56 mi719,339
DuPage CountyIllinois44 mi934,298
Will CountyIllinois41 mi712,253
Lake CountyIndiana36 mi504,612
Berrien CountyMichigan27 mi152,444
Kane CountyIllinois13 mi525,757
McHenry CountyIllinois2.0 mi317,751
Porter CountyIndiana0.7 mi176,049

Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.

Side by side

All 102 counties of Illinois

Open the interactive Illinois county map, or jump straight to any of them.

Data on this page last rebuilt 30 August 2026. How these figures are produced.