The Mariposa County Historical Society held its first meeting on April 14, 1957. In 1958 the museum was established at the Historic Masonic Lodge located nearby, and in December 1969 Judge Thomas and Katherine Coakley donated the land to the Mariposa County Historical Society. In 1972 the museum's collection was moved to this site. Outdoor exhibits include the five stamp mill from the Golden Key Mine, which crushed gold bearing ore in the Whitlock Mining District until 1953; the Counts House, built in 1863 by Augustus Shriver and purchased by County Treasurer George Counts in 1872; and the Gazette Building, which served as both the Sons of Temperance Hall and Mensing's Saloon before becoming the home of the Mariposa Gazette newspaper in 1875. Donated by the Campbell family in 1991, the Gazette Building includes some of the original type and presses, which are still used to print specialty items.