Mount St. John is a 150-acre property located in Beavercreek, Ohio owned by the Society of Mary (Marianists), a Catholic community of brothers and priests. The Marianists have lived and ministered at Mount St. John since 1910. The property is named for St. John the Apostle, patron of the Society of Mary. Mount St. John is home to residential communities of Marianist Brothers and Priests, the Marianist Environmental Education Center, the North American Center for Marianist Studies, the Marianist Mission, the Bergamo Center for Lifelong Learning, Gallery St. John, Queen of Apostles parish, and a 100-acre preserve. The buildings and grounds that are not part of the 100-acre preserve are maintained by Mount St. John Facilities.

The first people to care for this land were hunters, ancestors of the later Indian nations, from whom this was part of the sacred hunting grounds between the Miamis. Among the first Euro-Americans to arrive in this area were John Patterson and his family, who provided the land on which the Watervliet Shaker community was founded in 1806. The original 80 acres of Mount Saint John formed part of the East Farm of the Shakers and was purchased by the Marianists in 1910.

The nature preserve was dedicated as a State Natural Landmark in 1988. Staff and volunteers maintain 1.2 miles of nature trails that provide access to the prairie, woodlands, and wetlands for residents and guests of Mount Saint John.