Chelmsford is a town in Middlesex County, Massachusetts, United States. Chelmsford was incorporated in May 1655 by an act of the Massachusetts General Court. When Chelmsford was incorporated, its local economy was fueled by lumber mills, limestone quarries, kilns. In the 1700s, the Chelmsford militia played a role in the American Revolution at the Battle of Lexington and Concord and the Battle of Bunker Hill.