The museum building is a reconstruction of the Wells Fargo & Company Assay Office built in 1860 by Palmer & Day, who were Wells Fargo agents in Folsom. In 1959, one year short of its 100th birthday, the structure was torn down to make way for a gas station. In 1960, residents founded the Folsom Historical Society and in 1976 rebuilt the building on its original site as a museum.
In 1991, the Society dedicated the two-story addition on the adjacent lot, where Pony Express horses were once stabled.
