As Puerto Rico deals with the aftermath of Hurricane Maria, which has left millions without power, some are wondering: Is Puerto Rico part of the U.S.? Puerto Rico, an island in the Caribbean Sea, has been a territory of the United States since 1898, after the U.S. defeated Spain in the Spanish-American war. It's classified as an "unincorporated territory," meaning the island is controlled by the U.S. government but is separate from the mainland.