Clarkstown is a town in Rockland County, New York, United States. The town is on the eastern border of the county, located north of the town of Orangetown, east of the town of Ramapo, south of the town of Haverstraw, and west of the Hudson River. As of the 2010 census, the town had a total population of 84,187. The community of New City, the county seat of Rockland County, is also the seat of town government and of the Clarkstown Police Department, the county sheriff's police office, and the county correctional facility. New City makes up about 41.47% of the town's population.
In 2008, Clarkstown became one of 600 municipalities nationwide to sign the United States Mayor's Climate Protection Agreement to reduce carbon dioxide emissions to 7 percent below the 1990 levels by 2012.
The town of Clarkstown was created in 1791 in Orange County, before Rockland County was formed.
The Hudson River defines the eastern border of the town, which is opposite the town of Mount Pleasant in Westchester County.
According to the United States Census Bureau, the town has a total area of 46.9 square miles (121 km2), of which 38.5 square miles (100 km2) is land and 8.4 square miles (22 km2) (17.87%) is water.
The New York State Thruway (Interstate 87/Interstate 287) intersects the Palisades Interstate Parkway in the town.