The University of Dayton is a private, Catholic research university in Dayton, Ohio, United States. Founded in 1850 by the Society of Mary, it is one of three Marianist universities in the US and the second-largest private university in Ohio. Its campus is located in southern Dayton and spans 388 acres on both sides of the Great Miami River. The campus is noted fâŚThe University of Dayton is a private, Catholic research university in Dayton, Ohio, United States. Founded in 1850 by the Society of Mary, it is one of three Marianist universities in the US and the second-largest private university in Ohio. Its campus is located in southern Dayton and spans 388 acres on both sides of the Great Miami River. The campus is noted for the Immaculate Conception Chapel and the University of Dayton Arena.