The Principia College Historic District is a National Historic Landmark District encompassing the central portion of the campus of Principia College in Elsah, Illinois. The campus master plan, as well as eleven of its buildings, are important late designs of architect Bernard Maybeck, best known for his influential architecture in the American West. The Principia was declared a National Historic Landmark in 1993., and was also placed on the National Register of Historic Places that same year.