Prince George's County Historical Society - Frederick DeMarr His 11 Crescent Rd, Greenbelt, MD20770 The Prince George's County Historical Society is a group interested in preserving and learning more about Prince…More George's County and Maryland History. This group maintains the Frederick DeMarr Historical Library, which is located inside of the Greenbelt Library on the lower level. It has been at this location for two years. Frederick DeMarr was once the president and historian of the society. The historical society meets at Marietta Mansion located at 5626 Bell Station Road in Glenn Dale.