The Gators found themselves being pressed in the first half by the Demons, who were within eight at the break. Thoughts of an upset vanished in the second half, especially during a stretch in which Florida held Northwestern State scoreless for 6 1/2 minutes.
Florida (28-7), the third seeded team in the South Region, will now face Minnesota, which crushed UCLA 83-63.
Patric Young added 16 points for the Gators, who had 15 offensive rebounds to just three for the Demons. Florida held Northwestern State to 15 points in the second half.
The Demons reached the NCAA Tournament by winning the Southland Conference tourney as the No. 2 seed.
DeQuan Hicks was the only player for Northwestern State (23-10) to get to double figures with 12 points.