Madison County is a county located in the north central portion of the U.S. state of Alabama. As of the 2020 Census, the population was 388,153, and according to a 2023 population estimate the county has become the second-most populous county in Alabama after only Jefferson County, home to Birmingham. Its county seat is Huntsville. Since the mid-20th century it has become an area of defense and space research and industry. The county is named in honor of James Madison, fourth President of the United States and the first President to visit the state of Alabama. Madison County covers parts of the former Decatur County. Madison County is included in the Huntsville, Alabama Metropolitan Statistical Area.