is a hamlet (and a census-designated place) in Suffolk County, New York, United States. The population was 13,286 at the 2000 census. Students primarily attend the Harborfields Central School District.
Originally known as Old Fields, it became better known by the name Greenlawn (origin unknown) in the late 1800s. Greenlawn was well known for its pickle production during the 19th century as well as, to a lesser degree, potato and cabbage farms; the principal commodity, pickles, is still celebrated by the annual Pickle Festival, held by the local Greenlawn-Centerport Historical Association at the John Gardiner Farm.