Huntsville is a city located primarily in Madison County in the Appalacian region of northern Alabama. Huntsville is the county seat of Madison County. The city extends west into neighboring Limestone County. Huntsville's population was 180,105 as of the 2010 census. Huntsville is the fourth-largest city in Alabama and the largest city in the five-county Huntsville-Decatur-Albertville, AL Combined Statistical Area, which at the 2013 census estimate had a total population of 683,871.