Notre Dame hit 62 percent from the field and made 8-of-16 from beyond the arc in winning its 10th straight game. The Fighting Irish (12-2) are 10-0 at home this season.
The Notre Dame lead was only one point with 8 minutes to go in the opening half, but the Fighting Irish then closed the period on a 17-10 run and were not threatened over the final 20 minutes.
Cooley made 9-of-12 from the field and all six of his free throw attempts. Cameron Biedscheid added 15 points for Notre Dame and Jerian Grant had 13.
Niagara was led by 17 points from Antoine Matson.
Notre Dame made 12 more free throws than did the Purple Eagles (5-7) and recorded 12 more rebounds.