Middleton is a town in Essex County, Massachusetts, United States. The population was 8,987 at the 2010 census. Middleton is one of the fastest growing towns in the Commonwealth, and the fastest on the North Shore. When locally grouped it is grouped with Salem, Danvers, and Beverly, but also occasionally Topsfield and Boxford, as these three towns are a tri-town. These three towns share Masconomet Regional High School (named after Chief Masconomet, Sagamore of the Agawam tribe, which lived in Essex County at the time of English colonization) which serves grades 9-12, while its Middle School serves grades 7 and 8.