Cook County, Illinois

Cook County, Illinois
The century-old, neoclassical County and City Hall building (left) in the Chicago Loop houses the County Board chambers and administrative offices. The Chicago Picasso stands in front of Daley Center, the home of Cook County Circuit Court.
The century-old, neoclassical County and City Hall building (left) in the Chicago Loop houses the County Board chambers and administrative offices. The Chicago Picasso stands in front of Daley Center, the home of Cook County Circuit Court.
Flag of Cook County, Illinois
Official seal of Cook County, Illinois
Location within Illinois
Location within Illinois
Illinois' location within the United States
Illinois' location within the United States
Coordinates: 41°48′31″N 87°53′20″W / 41°48′31″N 87°53′20″W / 41.80861; -87.88889
CountryUnited States
RegionNorthern Illinois
Metro areaChicago Metropolitan
IncorporatedJanuary 15, 1831
Named forDaniel Cook
County seatChicago
Largest cityChicago
Incorporated municipalities
 • TypeCounty
 • BodyBoard of Commissioners
 • Board PresidentToni R. Preckwinkle (D)
 • County Board17 commissioners
 • County1,635 sq mi (4,230 km2)
 • Land945 sq mi (2,450 km2)
 • Water690 sq mi (1,800 km2)
 • Metro
10,874 sq mi (28,160 km2)
Area rank6th largest county in Illinois
Highest elevation950 ft (290 m)
Lowest elevation580 ft (180 m)
 • County5,194,675
 • Estimate 
 • Rank1st most populous county in Illinois
2nd most populous county in U.S.
 • Density3,200/sq mi (1,200/km2)
 • Metro
Time zoneUTC−6 (Central)
 • Summer (DST)UTC−5 (Central)
ZIP Code prefixes
Area codes224/847, 312/872, 773/872, 708
Congressional districts1st, 2nd, 3rd, 4th, 5th, 6th, 7th,
8th, 9th 10th and 11th
FIPS code17-031
GNIS feature ID1784766
InterstatesI-55.svg I-57.svg I-80.svg I-88.svg Chicago Skyway logo.svg I-90.svg I-94.svg I-190.svg I-290.svg I-294.svg I-355.svg
U.S. RoutesUS 6.svg US 12.svg US 14.svg US 20.svg US 30.svg US 34.svg US 41.svg US 45.svg US 66 (historic).svg
State RoutesIllinois 1.svg Illinois 7.svg Illinois 19.svg Illinois 21.svg Illinois 25.svg Illinois 38.svg Illinois 43.svg Illinois 50.svg Illinois 53.svg Illinois 56.svg Illinois 58.svg Illinois 59.svg Illinois 62.svg Illinois 64.svg Illinois 68.svg Illinois 72.svg Illinois 83.svg Illinois 110.svg Illinois 171.svg Illinois 390.svg Illinois 394.svg
AirportsChicago O'Hare International
Chicago Midway International
Chicago Executive
Lansing Municipal
Schaumburg Regional
Major WaterwaysLake Michigan – Chicago River
Chicago Sanitary and Ship Canal
Calumet River – Des Plaines River
North Shore Channel

Amtrak stationsChicago Union Station
Glenview – Homewood
La Grange – Summit
Public transitChicago Transit Authority (CTA)
Metra – Pace –
Demographics (2010)[4]
(any race)

Cook County is a county in the U.S. state of Illinois. It is the second-most-populous county in the United States after Los Angeles County, California. As of 2018, the population was 5,180,493. Its county seat is Chicago, the most populous city in Illinois and the third-most-populous city in the United States. More than 40% of all residents of Illinois live in Cook County.

Cook County's population is larger than that of 28 individual U.S. states, and the combined populations of the seven smallest states.[5] The county was incorporated by the state in 1831, and there are 135 separately incorporated municipalities partially or wholly within Cook County, the largest of which is Chicago, which is home to approximately 54% of the population of the county.

That part of the county which lies outside the Chicago city limits is divided into 29 townships; these often divide or share governmental services with local municipalities. Geographically, the county is the sixth-largest in Illinois by land area. It shares the state's Lake Michigan shoreline with Lake County. Including its lake area, Cook County has a total area of 1,635 square miles (4,234.6 km2), the largest county in Illinois, of which 945 square miles (2,447.5 km2) is land and 690 square miles (1,787.1 km2) (42.16%) is water. Land-use in Cook County is mainly urban and densely populated.

Cook County is included in the Chicago–NapervilleElgin, IL–INWI Metropolitan Statistical Area. It is surrounded by what are known as the five collar counties.


Cook County was created on January 15, 1831, out of Putnam County by an act of the Illinois General Assembly. It was the 54th county established in Illinois and was named after Daniel Cook, one of the earliest and youngest statesmen in Illinois history. He served as the second U.S. Representative from Illinois and the state's first Attorney General. In 1839, DuPage County was carved out of Cook County.

Other Languages
Bân-lâm-gú: Cook Kūn (Illinois)
български: Кук (окръг)
বিষ্ণুপ্রিয়া মণিপুরী: কোক কাউন্টি, ইলিনয়স
Bahasa Indonesia: Cook County, Illinois
پنجابی: کک کاؤنٹی
Plattdüütsch: Cook County (Illinois)
Simple English: Cook County, Illinois
српски / srpski: Округ Кук (Илиноис)
srpskohrvatski / српскохрватски: Cook County, Illinois
Tiếng Việt: Quận Cook, Illinois
粵語: 曲縣