The Town of Clarkstown was created by an act of the New York State Legislature on March 18, 1791, during Washington's first term of office. Since Rockland County was not created until 1798, Clarkstown was first a Town in Orange County before it became a Town in Rockland County.

In 1791 the population of Clarkstown was under 2000. In 1950 Clarkstown's population was approximately 15,000. With the opening of the Tappen Zee Bridge in 1955, the Palisades Interstate Parkway, and the Garden State Parkway extension, Clarkstown rapidly grew in population during the 1950s, 1960s and 1970s. As of the year 2000 census, Clarkstown's population was 82,082. Clarkstown ranks 15th in population of New York State's 932 towns.

Clarkstown is located 25 miles from midtown Manhattan, and New City is the seat of both Town Government and Rockland County Government. The Town encompasses approximately 41 square miles and includes the hamlets of Bardonia, Central Nyack, Congers, Nanuet, New City, Rockland Lake, Valley Cottage, West Nyack, all of the Village of Upper Nyack, and portions of the Villages of Nyack and Spring Valley. Clarkstown has almost 300 miles of roads, which are maintained by the Town's Highway Department, and an extensive park system that continues to expand as the Town acquires additional lands under the Open Space program.