Syosset is a hamlet (and a census-designated place) in Nassau County, New York, in the northeastern section of Town of Oyster Bay near the North Shore of Long Island. The population was 18,544 at the 2000 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.
Syosset is located at 40°48′46″N 73°30′03″W / 40.812743°N 73.500949°W / 40.812743; -73.500949.
According to the United States Census Bureau, the CDP has a total area of 5.0 square miles (12.9 km2), all land.