New Castle is a town in Westchester County, New York, United States. The population was 17,569 at the 2010 census.
New Castle has several locations on the National Register of Historic Places, including The Williams-DuBois House, Old Chappaqua Historic District, and Isaac Young House.
According to the United States Census Bureau, the town has a total area of 23.5 square miles (61 km2), of which 23.2 square miles (60 km2) is land and 0.3 square miles (0.78 km2), or 1.15%, is water.