The fire happened early Sunday morning at the Occupy BloNo campsite between Milner Library and the Bone Student Center.
No one was hurt, but a large tent was destroyed. A canopy that stretched over the campsite was also damaged.
NFD Spokesman Matt Swaney told WMBD 31 the investigation into the cause of the fire is ongoing.
But he also said it has been determined someone set the fire intentionally. Anyone with information is encouraged to call McLean County Crime Stoppers at (309) 828-1111.
Meanwhile, members of Occupy BloNo gathered at the former campsite Monday to talk about the future of the group.
Jennifer Carrillo admitted the group had not been very active since it formed in the fall.
"Many of us wanted to stay out here in the winter, but it got cold and we just couldn't do it. Some of our members were first time protestors, so we stumbled through," she said.
The group suspected the fire as arson from the get go. Carrillo said the campsite had been vandalized several times before.
"It's not surprising someone would do this," she said.
Now the incident has re-energized some of the members to tackle new challenges. They're forming a group based on what they call direct democracy.
The first meeting is set for May.
Carrillo said, "We tried some tactics. I think Occupy accomplished what it wanted to. We made ourselves difficult to ignore and we confronted a lot of people with the issues we face, and now it's time to use some new tactics."
Damage estimates to ISU's property were not immediately available.