Techstars in Chicago is actually less than 2 years old. Excelerate labs was 2 years old at the time it joined Techstars, so the oldest company connected to that city is less than 4.
Also important to control for cohort size. These are 10 company classes. A 100 million+ breakout seems to be somewhere between a 1 in 100 and a 1 in 50 occurrence.
Given that I work with our cloud program and in Austin I'm not as intimate with the alumni from Chicago, but one that I am personally fond of is http://www.giveforward.com/
They've crowd-funded over 125 million dollars toward medical expenses for people in need.
I'm a Chicagoan and and as jaredmck mentioned, there aren't any breakout successes. However, there are a number of companies are gaining steam like FoodGenius, Simple Relevance, and TempoIQ. Here's a link to the legacy Excellerate Portfolio: http://exceleratelabs.com/portfolio/
I think it's safe to say that's the answer - SpotHero is doing quite well and just raised a $4.5M series A, GiveForward as mentioned has crowdfunded a good amount of money for people's medical bills, and FeeFighters sold to groupon relatively early on. None of these are "breakout successes" to the tune of a 100M valuation, however.
Chicago startup scene has not generated a ton of hits, but there have been a few notable successes. But there are also a lot of solid companies that will probably make money for investors. You have to realize that there are very few Facebooks, AirBnBs and Ubers in total and most of them are by definition in SV. So you would expect relatively few out of Chicago at this point
Also important to control for cohort size. These are 10 company classes. A 100 million+ breakout seems to be somewhere between a 1 in 100 and a 1 in 50 occurrence.