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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.
Find information and services for Cook County residents, businesses and visitors. Learn about Project Rainbow, discount parking, manufacturing apprenticeships, solid waste and more.
Learn about the history, population, government and services of Cook County, the second most populous county in the nation. Cook County contains 134 municipalities, including the City of Chicago, and is governed by a 17-member Board of Commissioners.
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.
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.
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.
Learn about the population, diversity, economy, education, and health of Cook County, IL, the most populous county in Illinois and home to Chicago. See charts, maps, and data sources for various indicators and compare with other geographies.
