Syosset is a hamlet in Nassau County, New York, in the northeastern section of Town of Oyster Bay near the North Shore of Long Island. The population was 18,829 at the 2010 census. It is served by the Syosset railroad station, the Syosset Post Office, the Syosset Central School District, the Syosset Public Library, the Syosset Fire Department, and the Jericho Water District.