Mastic is a hamlet and census-designated place (CDP) in Suffolk County, New York, United States. The population was 15,481 at the 2010 census. Mastic is in the southeastern part of the town of Brookhaven.
The hamlet was originally called Forge. The Long Island Rail Road built a station in 1882. In 1893, the name of the hamlet was changed to Mastic. On July 15, 1960, the stop was moved west and renamed Mastic–Shirley.
The Poospatuck Indian Reservation lies entirely within the community, near its southern end.