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.

Poospatuck is situated in the southeast corner of Suffolk County's present-day Town of Brookhaven; and is the township's sole Indian reservation.

On account of the innumerable tobacco shops, the reservation is known synecdochally as "Mastic Boges" by those in neighboring towns.

The reservation and its people are recognized as Native American by the state of New York but it has not received federal recognition from the US Bureau of Indian Affairs.

However, the Unkechaug established that it met the criteria of a Tribe as set out in the Supreme Court case Montoya v. United States, 180 U.S. 261, 266 (1901).

The Unkechaug proved beyond a preponderance of the evidence that they met the criteria of a common law definition of a tribe consisting of the following: In a 2009 case, federal District Judge Kiyo Matsumoto held that the Unkechaug satisfied all 3 Montoya criteria thereby entitling the Unkechaug to Sovereign Immunity from lawsuits because they are a federal Tribe under federal common law.