Mexican island in the Caribbean Sea, located approximately 20 km east from the Yucatan peninsula. It belongs to the 10 municipalities of the Mexican state of Quintana Roo. Cozumel is a tourist resort popular among diving enthusiasts. The main city on the island is San Miguel de Cozumel. The island lies about 10 km (6.2 miles) from the mainland and 90 km (56 miles) south of Cancún. In 2016, a biosphere reserve was established there.