Madison County is a county in the U.S. state of Illinois. It is a part of the Metro East in southern Illinois. According to the 2020 census, it had a population of 264,776, making it the eighth-most populous county in Illinois and the most populous in the southern portion of the state. The county seat is Edwardsville, and the largest city is Granite City.

The Metro East is an urban area in Southern Illinois, United States that contains the eastern and northern suburbs and exurbs of St. Louis, Missouri. It encompasses five counties in the Greater St. Louis area and constitutes the second-most populous urban area in Illinois. The region's most populated city is Belleville, with 42,404 residents.