Conservation police are warning people not to park on the highways if parking fills up at Starved Rock and Matthiessen state parks over the holiday weekend.
Captain Laura Petreikis says people should come with a backup plan.
Both parks will be closed once their parking lots are filled.
To avoid backups on Routes 178 and 71 people are encouraged to go though Ottawa, cross the Illinois River and take Route 71 to the park.
Other parks in the area include Buffalo Rock State Park just west of Ottawa and Illini State Park in Marseilles.
Visitors should carry hand sanitizer, practice social distancing, and wear a mask.
Closure information will be posted on the Illinois Department of Natural Resources social media pages.