Huntsville is the most populous city in the U.S. state of Alabama. The population was 215,006 at the 2020 census, making it the 100th-most populous city in the U.S., while the Huntsville metropolitan area has an estimated 542,000 residents and is the second-most populous metropolitan area in the state. Huntsville is the seat of Madison County, with portions extending into Limestone County and Morgan County. Huntsville is located in the Appalachian region of northern Alabama, south of the state of Tennessee. It was founded within the Mississippi Territory in 1805 and became an incorporated town in 1811. When Alabama was admitted as a state in 1819, Huntsville was designated for a year as the first capital, before the state capitol was moved to more central settlements. The city developed across nearby hills north of the Tennessee River, adding textile mills in the late nineteenth century. Major growth in Huntsville took place in the decades following World War II. During the war, the U.S. Army established Redstone Arsenal in the vicinity, with a chemical weapons plant and related facilities. After the war, additional research was conducted at Redstone Arsenal on rockets, followed by adaptations for space exploration. NASA's Marshall Space Flight Center, the United States Army Aviation and Missile Command, and most recently the FBI's operational support headquarters, all were sited at Redstone Arsenal.