I checked with the forest services for dupage and cook county. Open air tents are allowed.
Just had a work event in early June (2018) and had a tent set up next to the wooden structure. Park ranger had no problem with it when she stopped by. I believe a tent is fine to set up.
They have one of those standing wooden 'party tent' shaped structures I forget what they are called (maybe the word I'm looking for is gazebo) , and have multiple picnic be benches underneath the structure
Im not sure but I would think so its tge forest preserve. Im pretty sure tou you can.
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