The University of Dayton (UD) 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. As of 2026, the university enrolls students from a variety of religious, ethnic and geographic backgrounds, totaling approximately 10,506 undergraduates and postgraduates combined, making UD the eleventh largest Catholic university in terms of enrollment in the U.S. It offers more than 80 academic programs in the arts, sciences, business, education, health sciences, engineering, and law.