Arecibo, town, northern Puerto Rico. It lies on a small inlet near the mouth of the Arecibo River. One of the oldest municipalities in the commonwealth, it was authorized in 1537 by the Spanish crown and settled in 1556. In 1616 it was chartered as a town and in 1778 received the royal title villa. An official U.S. port of entry, the town has Puerto Rico’s largest rum distilleries and produces agricultural machinery, clothing, paper, plastics, and sporting goods; it is linked to San Juan by a highway. The town has regional colleges of the University of Puerto Rico and the Inter-American University. South of Arecibo was one of the world’s most powerful radar-radio telescopes, the Arecibo Observatory, a 1,000-foot (305-metre) installation used for astronomical research from 1963 until just before its collapse in 2020. Pop. (2000) 49,318; (2010) 44,191.