Old Illinois license plate still used...?

a few days ago I saw an old style Illinois plate on someones car. The format which displays Illinois on the left, and Land of Lincoln on the right with 3 blue lines underneath. If I remember correctly they were displaying a 2011 sticker. After talking to my neighbor cop, he said he never had a problem running them, but was not sure if it's the same for a state trooper. Does anybody know if it's legal to still display theses plates on highways? And have you see any still on the road?