Carlisle is a town northwest of Boston located in Middlesex County, Massachusetts, United States. As of the 2010 U.S. Census, the population of the town was 4,852. According to the United States Census Bureau, the town has a total area of 15.5 square miles (40 km2), of which 15.4 square miles (40 km2) is land and 0.2 square miles (0.52 km2) (1.09%) is water. English colonialists first settled the area composing the town of Carlisle in 1651 on parcels of land of the neighboring towns of Acton, Billerica, Chelmsford and Concord. Carlisle became a district of Concord in 1780 and was officially incorporated as a town in 1805.