Mount Sinai is a hamlet and census-designated place located within the Town of Brookhaven in Suffolk County, New York, United States. The population was 12,118 at the 2010 census. The hamlet is located on the North Shore of Long Island, and is served by the Mount Sinai School District and the Mount Sinai Fire Department, founded on October 25, 1930. The Mount Sinai Fire District covers approximately 5.5 square miles including the Mount Sinai Harbor and parts of the Long Island Sound. Mount Sinai's ZIP code is 11766.Mount Sinai was first settled in the 1660s and was known by the name of Old Mans until a name change in the 1840s. Initially an agricultural hamlet, it transitioned into a popular resort town in the late-19th century and developed into a suburb of New York City in the mid-20th century. While primarily a residential community, the hamlet contains Mount Sinai Harbor and its popular public beach, Cedar Beach.