Mona is the third-largest island of the Puerto Rican archipelago, after the main island of Puerto Rico and Vieques. It is the largest of three islands in the Mona Passage, a strait between the Dominican Republic and Puerto Rico, the others being Monito Island and Desecheo Island. It measures about 7 miles by 4 miles, and lies 41 mi (66 km) west of Puerto Rico, of which it is administratively a part. It is one of two islands that make up the Isla de Mona e Islote Monito barrio in the municipality of Mayagüez.

Puerto Rico, officially the Commonwealth of Puerto Rico, is a Caribbean island, Commonwealth, and unincorporated territory of the United States. It is located in the northeast Caribbean Sea, approximately 1,000 miles (1,600 km) southeast of Miami, Florida, between the Dominican Republic and the U.S. Virgin Islands, and includes the eponymous main island and several smaller islands, such as Mona, Culebra, and Vieques. With roughly 3.2 million residents, it is divided into 78 municipalities, of which the most populous is the capital municipality of San Juan. Spanish and English are the official languages of the executive branch of government, though Spanish predominates.