Today's Gambrill Mill tract was historically part of a large land holding originally owned by James Marshall. The Gambrill Mill (also known as Araby Mill) was built in 1830, and purchased by James H. Gambrill in 1855 (the mill may be seen below right in an 1893 photograph). Gambrill owned and operated the mill into the 1890s and transformed it into a successful operation despite the disruptions caused by the Battle of Monocacy and subsequent use of the mill as a field hospital.
Originally, Gambrill Mill was a three-story merchant flour mill fitted with two pairs of "burr" or flour-milling stones. The mill's inside, undershot water wheel was powered by a millrace fed by nearby Bush Creek. The creek was dammed about a mile from the mill, and a sluice gate regulated the amount of water that was allowed to flow into the millrace. Remnants of the tailrace may still be seen at the front of the building. In addition to the flour mill, the complex also included a sawmill, a chopping and plaster mill, and a one-and-one-half story miller's house, along with a variety of other support structures.