Shelter Island is an island town in Suffolk County, New York, United States, near the eastern end of Long Island. The population was 3,253 at the 2020 United States census.

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.