Tourism to Chicago

Does anybody have info regarding how many tourists visit Chicago yearly and where they come from? How does Chicago compare to other US cities? What is the breakdown regarding business/leisure tourists, etc.? I am asking because today's tribune has an article regarding the weakening American dollar vs. the Euro and how European tourists have an advantage shopping abroad here in the US. The article mainly discusses Europeans shopping in NYC, but I am curious how much Chicago would also benefit from the increased spending? Any info/thoughts?>