The locations of Mary Ann Furnace, Mary Ann Furnace Speedway and a mystery site, possibly connected to Mary Ann Forge, are examined in this post. All locations are presently within the southwest end of Codorus State Park, about three miles southeast of Hanover. Mary Ann Furnace was the first cold-blast iron furnace west of the Susquehanna River. The furnace started operating 1761-62; three years before the startup of Codorus Furnace, located in Hellam Township. Different Signers of the Declaration of Independence were owners of these two furnaces, which produced munitions during the Revolutionary War.