Cook County area

Population and density of Cook County

The Census Bureau estimates that 5,194,625 people lived in Cook County on July 1, 2025. That ranks #2 of 3,222 county equivalents nationally and #1 of 102 in Illinois. Since the April 1, 2020 estimates base of 5,279,010, the population has declined by 84,385 (−1.6%), compared with −0.8% for Illinois as a whole.

With 944.9 square miles of land, that is 5,497 people per square mile (2,123 per km²), placing Cook County #18 nationally for density and #1 in Illinois. The median county equivalent has 47 people per square mile; the Illinois median is 44. Put another way, there are about 0.116 acres of land per resident.

U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.

Cities and towns in Cook County

137 incorporated places lie at least partly in Cook County. Together they are home to 5,093,285 people (98%); the other 101,340 (2%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Chicago city, with 2,731,585 residents in the county (the city extends into 1 other county). Among places with at least 1,000 residents in 2020, Lemont village grew fastest since then (+4%).

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Cook County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.

Metropolitan area

Cook County is a central county of the Chicago-Naperville-Elgin, IL-IN Metropolitan Statistical Area, in the Chicago-Naperville-Schaumburg, IL metropolitan division. Its 13 county equivalents have 9,434,123 residents on 6,923.3 square miles of land; Cook County accounts for 13.6% of the land and 55.1% of the residents. By combined land it ranks #27 of 393 metropolitan areas, and #3 by population. It belongs to the Chicago-Naperville, IL-IN-WI Combined Statistical Area.

ZIP codes

178 ZIP Code Tabulation Areas have land in Cook County; 167 of them have most of their land inside the county, and the others mainly cover neighboring areas.

60004600056000760008600106001560016600186002260025600266002960043600536005660062600676006860070600746007660077600896009060091600936010360104601076012060126601306013160133601416015360154601556016060162601636016460165601696017160172601736017660192601936019460195602016020260203602086030160302603046030560402604066040960411604156041860419604226042360425604266042860429604306043860439604436044560449604526045360455604566045760458604596046160462604636046460465604666046760469604716047260473604756047660477604786048060482604876050160513605216052360525605266052760534605466055860601606026060360604606056060660607606086060960610606116061260613606146061560616606176061860619606206062160622606236062460625606266062860629606306063160632606336063460636606376063860639606406064160642606436064460645606466064760649606516065260653606546065560656606576065960660606616070660707607126071460803608046080560827

ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.

Counties bordering Cook County

Cook County shares a land border with 6 county equivalents, including 1 in Indiana. It has more land than every one of them. The largest neighbor is Will County (835.9 mi²) and the smallest is DuPage County (327.9 mi²). Together with its neighbors, Cook County forms a block of 4,174.1 mi² of land, of which it holds 22.6%.

How big is Cook County compared with U.S. states?

Cook County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.1 times as much. Illinois’s county land could hold about 59 areas the size of Cook County.

Another way to picture it: the same land area would fill a square about 30.7 miles (49.5 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.

State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.

What stands out about Cook County?

Cook County has more land than 2,471 of the other 3,221 county equivalents in the dataset.

A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.

Does including water change its rank?

Using land plus water places Cook County at #412 nationally by total area, 339 places closer to the top than its land rank. The water assigned to this geography moves it ahead of some county equivalents with more land.

Its water share is 42.2%, compared with a national county-equivalent median of 1.2% — 41 percentage points higher. This describes the statistical geography’s land/water mix, not flood exposure or developable land.

Closest positions in the national land ranking

These entries sit immediately beside Cook County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.