Mattituck is a hamlet and census-designated place (CDP) in Suffolk County, New York, United States. The population was 4,584 in 2023 according to the World Population Review. Located in the Town of Southold, Mattituck CDP roughly corresponds to the hamlet by the same name.

The Town of Southold is one of ten towns in Suffolk County, New York, United States. It is located in the northeastern tip of the county, on the North Fork of Long Island. The population was 23,732 at the 2020 census. The town also contains a hamlet named Southold, which was settled in 1640.