For all intents and purposes, Chicagoland is Chicago when it comes to food. You don't need to head into the city proper to get your Chicago-style pizza, hot dogs, beef, steaks, and what have you. There are some Chicago-style fast-food locations outside the city that will serve you these items, prepared better than anywhere in the city. Same goes for many styles of ethnic food—you can get Mexican, Polish, Italian, Greek just as good or even better in the 'burbs. Some ethnic cuisines out here you would have trouble finding in the city—Uzbek, Russian, Afghan, etc.
For upscale cuisine, the hautest of the haute is still to be found downtown. But there are plenty of nice restaurants in places like Evanston especially, Naperville, and others.
