Huntsville is a city located primarily in Madison County in the Appalachian 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 third-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. The Huntsville Metropolitan Area's population was 417,593 in 2010 to become the 2nd largest in Alabama. Huntsville metro's population reached 441,000 by 2014.It grew across nearby hills north of the Tennessee River, adding textile mills, then munitions factories, NASA's Marshall Space Flight Center and the United States Army Aviation and Missile Command nearby at the Redstone Arsenal.