thumb|left|Early ONU buildings depicted on a postcard Before the Great Depression, more than one thousand students were typically enrolled at Ohio Northern every year. Both the Great Depression and the following World War II plunged the school into low enrollment, and the possibility of closure was considered. During World War II, enrollment reached a low of 156 students. Thanks to the G.I. Bill, Ohio Northern was able to bring enrollment back up to nine hundred students by 1946.
