San Juan, officially Municipio de la Ciudad Capital San Juan Bautista (Municipality of the Capital City, Saint John the Baptist), is the capital and most populous municipality in Puerto Rico, an unincorporated territory of the United States. As of the 2000 census, it has a population of 433,733, making it the 42nd-largest city under the jurisdiction of the United States. San Juan was founded by Spanish colonists in 1521, who called it Ciudad de Puerto Rico ("Rich Port City").