Westchester County is a county in the U.S. state of New York. Westchester covers an area of 450 square miles (1,200 km 2), consisting of 48 municipalities. According to the 2010 Census, the county had a population of 949,113, estimated to have increased by 2.5% to 972,634 by 2014. Established in 1683, Westchester was named after the city of Chester, England.