<Tr> <Th> Pop . density </Th> <Td> 610 / sq mi (236 / km) </Td> </Tr> <Tr> <Th> Ethnic groups </Th> <Td> Afro - Caribbean, Puerto Rican, Caucasian </Td> </Tr> <P> Saint Croix (/ ˌseɪnt ˈkrɔɪ /; Spanish: Santa Cruz; Dutch: Sint - Kruis; French: Sainte - Croix; Danish and Norwegian: Sankt Croix, Taino: Ay Ay) is an island in the Caribbean Sea, and a county and constituent district of the United States Virgin Islands (USVI), an unincorporated territory of the United States . </P> <P> St. Croix is the largest of the islands in the territory . However, the territory's capital, Charlotte Amalie, is located on Saint Thomas . As of the 2010 United States Census, St. Croix's population was 50,601, its highest point is Mount Eagle, at 355 metres (1,165 ft). St. Croix's nickname is "Twin City", for its two towns on opposite ends of the island, Frederiksted on the western end and Christiansted on the east . </P>

Is st. croix part of the us virgin islands