Old Westbury is a village in the towns of North Hempstead and Oyster Bay in Nassau County, on the North Shore of Long Island, in New York, United States. The population was 4,671 at the 2010 census. The Incorporated Village of Old Westbury is one of the wealthiest villages in the country as well as the second-richest zip code in the New York State, topped only by Harrison in Westchester County. In 2007, Business Week dubbed Old Westbury as New York's most expensive suburb.