Something very strange happens in Chicago on October 2nd every year. Not the end of the baseball season. Not the return of Oktoberfest beers. Not the announcement of the Oscar host. It's the end of the rental season, and it's arrival is both sudden and predictable. Don't believe me? Check out the Google Insights for people searching for "apartments" and "rentals" over the past 8 years.
Now check out the seasonal rental activity for a few select Chicago neighborhoods in the MLS going back to 2007, when rental listings were first added to the system:
You see those annual dips towards the end of the year? That's what I'm talking about. The most very basic law of economics - supply & demand - has caused the Chicago rental market to evolve into a very unbalanced annual cycle. This is not a chicken/egg paradox - lower demand definitely leads to lower supply and not the other way around. Personally I would think that this is due to many leases starting on the first of the month. Let's look at what happens on the first of the month in Chicago after October 1: