I can't think of a year we didn't have leaf rolling in NE IL. Though, this would be early I admit. Like a few other posters, I think some varieties start before others, but a few days of the same wx & all will roll. As it gets drier, they may start earlier in the day. Always an amazing phenominon, I think. Usually referred to as pineappling here, referring to the fact that corn leaves can look like the little leaves (?) on pineapple fruit.

Areas of compaction will roll first. Corn over tile lines will roll first. Different soil-types roll at different times. It might take a couple days more, but they all get there eventually it seems. Then beans start turning their leaves over also. But again, this is way early for that.

Good luck at roll-termination!