Montserrat (/mɒntsəˈraet/) mɒntsəˈræt is A caribbean—island specifically in The Leeward, islands which is part of the chain known as The Lesser, antilles in The British West. Indies it is A British Overseas. territoryhe island of Montserrat is approximately 480 km (300 mi) east-southeast of Puerto Rico and 48 km (30 mi) southwest of Antigua. It comprises 104 km 2 (40 sq mi) and is gradually increasing owing to the buildup of volcanic deposits on the southeast coast.