an island in the CaribbeanSea, southeast of the US state of Florida. Population: 3,674,209 (2014). Capital: San Juan. People who live in Puerto Rico are US citizens, but Puerto Rico is not a US state and it governs itself. Many people from Puerto Rico go to live and work in the US in order to earn more money. It was a colony of Spain from 1509 to 1898, and most people speakSpanish as their first language.