Union is a town in Tolland County, Connecticut, United States. The population was 854 at the 2010 census, making it the least populous town in Connecticut and the second-least populous municipality in Connecticut; only the Borough of Fenwick has fewer people. Union includes the village of Mashapaug located in the Eastern Uplands at the Massachusetts state line. The first white settlement in Union was in 1727, making Union the last Connecticut town east of the Connecticut River to be settled. The first settler was James McNall of Worcester, Massachusetts. He was closely followed by his brother William. The town was incorporated in October 1734.