[Kazan]

Has Indiana ever won a “national championship” during the AP/Coaches poll era?

No. In fact, Indiana has the most losses of any Division I school in college football history:

At the start of the college football season, no Division I program had more losses in its history than Indiana’s 715 defeats.

[Verginius Rufus]

Before yesterday, Indiana had lost 30 games in a row to Ohio State. Their total number of defeats by the Buckeyes is much larger but I don’t recall the number.