Lake County is a county in the northeastern corner of the U.S. state of Illinois, on the shore of Lake Michigan. According to the 2010 census, it has a population of 703,462, which is an increase of 9.2% from 644,356 in 2000. Its county seat is Waukegan. The county is part of the Chicago metropolitan area. According to the 2000 census, Lake County is the 31st richest county by per capita income.