Chicago actually has a very large Mexican population.

"The 2000 census counted more than 530,000 Mexicans in the city of Chicago, with more than 1.1 million in the metropolitan area."

http://www.encyclopedia.chicagohistory.org/pages/824.html

There are hole-in-the-wall Mexican restaurants everywhere in Chicago.

I live in Tucson and occasionally choose to eat at Chipotle none the less. There isn't a taco shop around that makes a veggie burro anywhere close to Chipotle's guacomole burrito. While a caloric load in itself, half a burrito is a good sized meal and is lighter than the comparison.

Is it Mexican? Not quite. Is it pretty tasty? For fast food, at least.

Chipotle is a national chain that is highly-profitable. Consider it the Starbucks of Mexican food. Not as good as the "local" place, but consistently okay everywhere you go.

Chipotle's specialty, San Francisco burritos, aren't Mexican, they are northern Californian :)

http://en.wikipedia.org/wiki/San_Francisco_burrito

I dare you to go to Pilsen and say that.

Rick Bayless is based in Chicago with Frontera Grill and is considered an expert in authentic Mexican food. He has won multiple James Beard awards including national chef of the year.