St. John ( ; ; ; ) is an island in the Caribbean Sea and a constituent district of the United States Virgin Islands (USVI), an unincorporated territory of the United States. The smallest of the main US islands, St. John is located about four miles east of Saint Thomas, the location of the territory’s capital, Charlotte Amalie. It is four miles southwest of Tortola, part of the British Virgin Islands. It is 50.8 km² (19.61 sq mi) in area with a population of 4,170 (2010 census). As of the 2010 U.S. Census, the total population of the island territory was 106,405, comprising mostly persons of Afro-Caribbean descent. Because there are no airports on St. John, the only access to the island is by boat. A ferry service runs hourly from St. Thomas and daily from Tortola; regular ferries also operate from Virgin Gorda, Jost Van Dyke and Anegada. Since 1956, approximately 60% of the island is protected as Virgin Islands National Park, administered by the United States National Park Service. The economy is based on tourism.