Waukegan is an industrial suburb located 36 miles north of Chicago. It is the most populous city and county seat of Lake County, Illinois, Unite…Waukegan is an industrial suburb located 36 miles north of Chicago. It is the most populous city and county seat of Lake County, Illinois, United States. As of the 2020 census, its population was 89,321, making it the seventh-most populous city within the Chicago metropolitan area and the 10th-most populous city in Illinois.