Our coverage area will be mostly Chicago initially (but you can take the cars anywhere you like) and the airports. As we grow you'll see our coverage expand.
Here is a map of our current (estimated) service area: http://goo.gl/rQgIQ .  For more info also check out uber.com/chicago .

Please keep in mind that once you're in a vehicle, you can take it wherever you like. Coverage area is where it's easiest to get picked up by a driver.