New Haven is a city in New Haven County, Connecticut, United States. It is located on New Haven Harbor on the northern shore of Long Island Sound and is part of the New York City metropolitan area. With a population of 135,081 as determined by the 2020 U.S. census, New Haven is the third largest city in Connecticut after Bridgeport and Stamford, the largest city in the South Central Connecticut Planning Region, and the principal municipality of Greater New Haven, which had a total population of 864,835 in 2020. Prior to 1960, it was the county seat of New Haven County until the county governments were abolished that year. New Haven was one of the first planned cities in the U.S. A year after its founding by English Puritans in 1638, eight streets were laid out in a four-by-four grid, creating the "Nine Square Plan". The central common block is the New Haven Green, a 16-acre (6 ha) square at the center of Downtown New Haven. The Green is now a National Historic Landmark, and the "Nine Square Plan" is recognized by the American Planning Association as a National Planning Landmark. New Haven is the home of Yale University, New Haven's biggest taxpayer and employer, and an integral part of the city's economy. Health care, professional and financial services and retail trade also contribute to the city's economic activity. The city served as co-capital of Connecticut from 1701 until 1873, when sole governance was transferred to the more centrally located city of Hartford. New Haven has since billed itself as the "Cultural Capital of Connecticut" for its supply of established theaters, museums, and music venues. New Haven had the first public tree planting program in the U.S., producing a canopy of mature trees (including some large elms) that gave the city the nickname "The Elm City".