Islip is a town in Suffolk County, New York, United States, on the South Shore of Long Island. The population was 335,543 at the 2010 census, making it the fourth most populous city or town in the New York metropolitan area.

Suffolk County is the easternmost county in the U.S. state of New York. It is bordered to its west by Nassau County, to its east by Gardiners Bay and the Atlantic Ocean, to its north by Long Island Sound, and to its south by Great South Bay. The county is part of the Long Island region of the state, of which it comprises the eastern two-thirds.