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 2020 census, the town had a total population of 86,855. The hamlet 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 office, and the county correctional facility. New City makes up about 41.47% of the town's population.

Rockland County is the second-southernmost county on the west side of the Hudson River in the U.S. state of New York, after Richmond County. It is part of the New York metropolitan area. As of the 2020 U.S. census, the county's population is 338,329, making it the state's third-most densely populated county outside New York City after Nassau and neighboring Westchester Counties. The county seat and largest hamlet is New City. Rockland County is accessible via the New York State Thruway, which crosses the Hudson to Westchester at the Tappan Zee Bridge ten exits up from the NYC border, as well as the Palisades Parkway five exits up from the George Washington Bridge. The county's name derives from "rocky land", as the area has been aptly described, largely due to the Hudson River Palisades. The county is part of the Hudson Valley region of the state.