10 Largest Cities In Alabama -- The Rocket City (Huntsville) Ranks Number 1 Nestled in the Appalachian region in northern Alabama is the majestic city of Huntsville, the state's most populous city . It encompasses parts of Madison, Limestone, and Morgan Counties but is the designated seat for Madison County ; and a former capital city. Nicknamed " Rocket City ," the Redstone Arsenal was erected here during World War II by the US Army. However, a significant population boom occurred after the war when the Redstone Arsenal turned to space exploration, focusing on rockets. This leap forward brought forth the NASA Marshall Space Flight Center, the United States Army Aviation and Missile Command, and even the FBI's operational support command center to the city. Huntsville continues to grow and, as of the most recent census, has a trajectory to expand by 1.60% annually. Reference: www.worldatlas.com