Cook County is the most populous county in the U.S. state of Illinois, located in the northeastern part of the state. It is also the second-most populous county in the United States after Los Angeles County, California. COOK County is home to the city of Chicago and its surrounding suburbs. The county seat is Chicago, and it is the most populous county in the state with a population of over 5 million people. COOK County is named after Daniel Pope COOK, an early Illinois statesman.