Lock 21 is called Swain’s Lock after the Swain family. Members of this family worked on the Chesapeake & Ohio canal since its construction and resided in Lockhouse 21 from 1924 through the early 2000s.
Construction on the 91-foot Lock 21 was begun in July 1829 and completed in October 1830 by the firm of Holdsworth and Isherwood for a total cost of $8,327.76. The Lock was built from red sandstone from the Seneca Quarry, Montgomery County, MD. A few of the stones in the lock wall can be identified with an individual stone cutter who used the mason’s mark, E*.
Built using an 1828 design, the Lock was intended to be filled with water by culverts in the walls. Because these culverts frequently became clogged with debris, lock gates with inset wickets—easier to maintain and replace—were added in the late nineteenth century. The water level in the Lock varied by approximately 8 feet.