Syosset is a hamlet and census-designated place (Syosset) in Nassau County, New York, United States, in the northeastern section of the Town of Oyster Bay, on the North Shore of Long Island. Syosset 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. The population was 18,829 at the 2010 census. Syosset is located approximately 32 miles (50 km) east of Midtown Manhattan, 14 miles (20 km) east of eastern border with Queens, 23 miles (40 km) southeast of the Throgs Neck Bridge, and 168 miles (270 km) southeast of Albany, the state capital. It is also in close proximity to beaches, with Jones Beach only 19 miles (30 km) south of the town. It borders Oyster Bay and Laurel Hollow to the north, Woodbury to the east, Plainview and Hicksville to the south, and Jericho and Muttontown to the west, Syosset is accessible to New York City by the LIRR and the Long Island Expressway by car.
Syosset is located at 40°48′46″N 73°30′03″W.
According to the United States Census Bureau, Syosset has a total area of 5.0 square miles (13 km2), all land.
As of the 2010 U.S. Census, there were 18,829 people, 8,131 households, and 5,307 families residing in Syosset. The population density was 3,719.7 per square mile (1,434.8/km2). There were 6,354 housing units at an average density of 1,274.5/sq mi (491.6/km2).