I've hunted in a lot of town parks in DuPage County over the years and never had a problem hunting at any of them. There are some excellent old town parks and old towns thereabouts, not to mention anywhere in those older areas where my first love, the sidewalk and street work construction sites may be ongoing. Stay out of Addison, that much I know. Didn't have any problem there but heard from others who did. Can't offer a list of which towns are okay because I don't stay up to date.
My usual practice is to go someplace and find the first passing uniform and ask them where all the good oldies are, they'll let you know what's on their minds regarding MD'ing pretty quick. Also ask park personnel if they've seen anyone else detecting around there lately, also a good way to get a quick answer without sounding like you're worried about whether or not you should be there.
Have fun!