There is no international checkpoint at the Wisconsin-Illinois border. No passport is required. No customs agent asks whether you are carrying contraband cheese curds or an excessive quantity of Spotted Cow.

But there is unquestionably a border.

Call it the Cheese Curtain, that invisible cultural line separating two states that share 200 miles of geography, millions of weekend trips and a relationship best described as neighborly — provided nobody mentions the Packers & Bears, Brewers and Cubs, property taxes, driving ability or who ruined Lake Geneva and Galena.

Wisconsin and Illinois need each other, vacation in each other’s states, work across the border and generally get along just fine. But where would be the fun in admitting that? We prefer the old jokes. What’s the best thing to come out of Illinois? I-94. What does FIB stand for? Well, we’ll get to that in a little bit.