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Cook County is the most populous county in the U.S. state of Illinois and the second-most-populous county in the United States, after Los Angeles County, California. More than 40 percent of all residents of Illinois live within Cook County. As of 2020, the population was 5,275,541.
Cook County contains 134 municipalities in its region, the most well known being the City of Chicago – which is the County seat where the central offices of Cook County are located.
Cook County was created on January 15, 1831 by an act of the Illinois State Legislature as the 54th county established in Illinois. The unincorporated Fort Dearborn settlement at the mouth of the Chicago River became the new county’s seat. On May 7, 1831, Cook County elected its first officials.
Cook County contains 134 municipalities in its region, the most well known being the City of Chicago – which is the County seat where the central offices of Cook County are located.
As the seat of Cook County, the second-most populous county in the U.S., Chicago is the center of the Chicago metropolitan area, often colloquially called "Chicagoland" and home to 9.6 million residents.
The government of Cook County, Illinois, is primarily composed of the Board of Commissioners, other elected officials such as the Sheriff, State's Attorney, Treasurer, Board of Review, Clerk, Assessor, Cook County Circuit Court judges and Circuit Court Clerk, as well as numerous other officers and entities.
In 2022, Cook County, IL had a population of 5.23M people with a median age of 37.5 and a median household income of $78,304. Between 2021 and 2022 the population of Cook County, IL declined from 5.27M to 5.23M, a −0.76% decrease and its median household income grew from $72,121 to $78,304, a 8.57% increase.
