Madison County is located in the north central portion of the U.S. state of Alabama. As of the 2020 Census, the population was 388,153, making it the third-most populous county in Alabama. 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.