Riverside is a hamlet and census-designated place (CDP) in Suffolk County, New York, United States.

[2] Riverside is in the Town of Southampton and derives its name from being on the south bank of the Peconic River.

[2][3] At the 2000 census,[5] there were 2,875 people, 846 households and 485 families residing in the CDP.

There were 926 housing units at an average density of 181.5 per square mile (70.1/km2).

36.5% of all households were made up of individuals, and 22.0% had someone living alone who was 65 years of age or older.