You can grow your own sunflowers for about $15 per acre. If you take sunflowers from Matthiessen State Park, you could be fined $195. The Illinois Department of Natural Resources has posted a warning at Matthiessen.
Visitors impressed by the vast sunflower field planted for the public’s enjoyment seem to think taking a few for themselves won’t hurt. But when a lot of people do it, it’s destructive. And it’s illegal to take any plant out of an Illinois state park anyway.