Mastic Beach is a hamlet and census-designated place, and former village in the southeastern part of the Town of Brookhaven in Suffolk County, on Long Island, in New York, United States. The population was 14,849 at the 2010 census, when it was an unincorporated census-designated place for the first time.

Brookhaven, formally the Town of Brookhaven, is a large suburban town in Suffolk County, Long Island, New York. With a population of 488,497 as of 2022, it is the second most populous town in the United States and in New York and the third most populous community in the state.