Chicago[a] is the most populous city in the U.S. state of Illinois and in the Midwestern United States. With a population of 2,746,388 in the 2020 census,[8] it is the third-most populous city in the United States after New York City and Los Angeles. 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.