Clarksville is a city in and the county seat of Montgomery County, Tennessee, and the fifth-largest city in the state behind Memphis, Nashville, Knoxville, and Chattanooga, respectively. The city had a population of 132,957 at the 2010 census, and an estimated population of 142,519 in 2012. Wikipedia

Huntsville is a city located primarily in Madison County in the central part of the far northern region of the State of 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. Wikipedia