Rock Run Grist Mill is located in the Susquehanna State Park in Havre de Grace, MD. The Mill was built in cir. 1764 by John Stump, a business man who owned several mills in Harford, Cecil and Baltimore Counties. The Mill is completely restored to its late 1800's to early 1900's splendor. The original Fitz Water Wheel was installed in 1900. As of June 2007- the mill is now in operation and is grinding corn for a local business in Bel Air, MD.