What is the smallest division 1 football school?

Presbyterian College (Clinton, SC) is the smallest Division I FCS (Football Championship Subdivision, formerly Division I-AA) school, with 1200 undergraduates.

The smallest Division I FBS (Football Bowl Subdivision, formerly Division I-A) school is the University of Tulsa, with 2756 undergraduates. Rice University is the second smallest, with 3054, and Wake Forest University is the third smallest, with 4412.