I was Assistant Director of Admissions in 1970-71 when we first started interviewing women to enroll at Notre Dame in 1972, but………that is not technically the correct answer to the question.
When I was in grad school in the late 60’s, the campus was full of black-robed nuns, so clearly there were women attending Notre Dame in grad school and summer sessions, so when did women first begin taking classes at Notre Dame.
I posed this question to my friend Peter Lysy, of the wonderful Notre Dame Archives. Here’s his answer:
Two women earned master’s degrees at the 11 June 1917 commencement. Eight more received MAs in 1918 (June and August). Women were first admitted to the Summer Session at its inauguration in 1918. Clearly, there were women receiving credit for work at Notre Dame even before Summer Session started, but I believe the nature of their work was more like directed readings/one-on-one work with professors, not attending classes with the boys. So when did ND first go co-ed? It all depends on your definition of "going coed", but it is clear that ND was educating women by the middle teens.
Editor's Note: We had St. Mary's girls in our Engineering classes in our Junior Year.