What age do you have to be to camp? Like could a few 16 year olds go unsupervised?

Illinois State Park policy is that a campsite may have one family, or up to four unrelated people over 18, so I'd say you're probably out of luck.

Dont ask dont tell and abide by rules😄

I'm pretty sure they would not have any troubles. The beach is unsupervised and patrolled every so often. I don't think it would be a huge concern as long as they weren't drawing negative attention to themselves... otherwise everything should be fine. I've seen some younger looking kids there by themselves in the past.

Usually not, most parks require someone to be 18 years old to camp