I've linked a guide to U-pick pumpkin patches in Illinois. Good stuff, and last weekend was perfect for searching out the perfect pumpkin.
We visited Butterprint Farm in Monee, maybe an hour or so from Chicago. They have two good-sized pumpkin patches, one planted earlier in the season so you have a nice range of sizes. Both are accessible after a short, extremely bouncy hay ride. They also have gourds, indian corn, nice looking pie pumpkins, apples, and honey.
The "Pollination Theatre" puppet show sounded great, but we missed the showing. Note: ladybugs were very bitey, and pumpkin stems have lots of hairy little thorns!
I found another link to small Illinois farms that sell directly to the consumer, everything from eggs, produce, honeys, to heirloom turkeys. Will post that link shortly.