East Caln originated in 1728 when the inhabitants of Caln Township petitioned to divide the town into East and West. During the 18th century, development filled the same pattern as in other townships in Chester County. People settled along rivers for the fertile soil and the use of water power for first and fulling mills, as well as saw mills. Development was greatly aided in East Caln by the construction of the Lancaster Turnpike, which opened in the last decade of the 18th century. The turnpike called easy trade with Philadelphia, Lancaster and points west. Not only did trade grow as a result of the roadway, but it made East Caln a witness to everything the happened in America. It was used by troops to West Pennsylvania to put down the whiskey rebellion, groups of people heading west with covered wagons, sites for political speeches, and men going off to war.
Though greatly opposed by the residents of East Caln, Downingtown petitioned to withdraw from the Township. The petition was granted and Downingtown was created as a Borough in 1859. For the next hundred years, East Caln had the threat of various townships petitioning for more land until 1968 when a law was passed which required the consent of both those wanting the land and those giving up the land. As a result, the boundaries of East Caln kept changing, leading to the recreation of the original township.