Old Westbury is a village in Nassau County, in the U.S. state of New York, on the North Shore of Long Island. As of the 2010 United States Census, the village population was 4,671.The Incorporated Village of Old Westbury is located in both the Town of Oyster Bay and the Town of North Hempstead.In 2007, Business Week dubbed Old Westbury as New York's most expensive suburb. Old Westbury Gardens has been recognized as one of the three best public gardens in the world by Four Seasons Hotels magazine.