The Harrisburg–Carlisle, Pennsylvania, metropolitan statistical area is defined by the United States Census Bureau as an area consisting of three counties in Pennsylvania's Susquehanna Valley, anchored by the cities of Harrisburg and (to a lesser-extent) Carlisle. As of the 2010 census, the metropolitan statistical area (MSA) had a population of 549,475 (though a July 1, 2009 estimate placed the population at 536,919). In 2009, Harrisburg–Carlisle was the 96th largest metropolitan area in the United States.