The Poospatuck Reservation is a Native American reservation of the Unkechaugi band in the community of Mastic, Suffolk County, New York, United States. It is one of two Native American reservations in Suffolk County, the other being the Shinnecock Reservation. The population was 436 at the 2020 census. The Unkechaugi are descendants of the Quiripi-speaking Native Americans, who occupied much of southern New England and central Long Island at the time of European encounter in the colonial era.