Huntsville is a city located primarily in Madison county in the central part of the far northern region of the U.S. state of Alabama. Huntsville is the county seat of Madison County. The city extends west into neighboring Limestone county. Its population was 158,216 as of the 2000 census, while in 2009, the estimated population grew to 179,653. The Huntsville Metropolitan Area's population was estimated at 406,316. Huntsville is the largest city in the four-county Huntsville-Decatur Combined Statistical Area, which in 2008 had a total population of 545,770.