Beautiful West Indies Island St.Lucia. Saint Lucia is a sovereign island country in the eastern Caribbean Sea on the boundary with the Atlantic Ocean.[5] Part of the Lesser Antilles, it is located north/northeast of the island of Saint Vincent, northwest of Barbados and south of Martinique. It covers a land area of 617 km2 (238.23 sq mi) and has a population of 174,000 (2010). Its capital is Castries.