Union Island is part of the nation of Saint Vincent and the Grenadines. It has a surface of 9 square kilometres (3.5 sq mi) and lies about 200 km west-southwest of Barbados within view of the islands of Carriacou and the mainland of Grenada, which lies directly south.

Saint Vincent and the Grenadines is an island country in the eastern Caribbean. It is located in the southeast Windward Islands of the Lesser Antilles, which lie in the West Indies, at the southern end of the eastern border of the Caribbean Sea, where the latter meets the Atlantic Ocean.