DeWitt County is a county located in the U.S. state of Illinois. As of the 2020 census, the population was 15,516. Its county seat is Clinton. The county was formed on March 1, 1839, from Macon and McLean counties. The county was named in honor of the seventh Governor of New York State, DeWitt Clinton. DeWitt County is included in Bloomington–Normal, IL Metropolitan Statistical Area. The U.S. Census Bureau and the U.S. Geological Survey list the county's name as De Witt, although the county uses the name DeWitt.