Seth and Philip brought up good points.
Craigslist is a great online source of information and furnished rentals are tough to come by because the northside of Chicago is predominantly not a furnished-rental type market. That doesn't mean you may not find a sweet gem of a place, but if you do, that will be further complicated by the short timeframe that you will be in Chicago. If you have not done so already, you might check out Domu.com or apartments.com for sublet and short-term rentals of furnished places.
Given the timeframe you are seeking, it is possible you could benefit from a current tenant who is traveling abroad or someone on a short-term assignment out of Chicago. You might also consider the building at Roscoe & Lincoln, it is a bit south of Winnemac Park, but I believe it offers furnished apartments.
You might also give TJ Rubin a call at Fulton Grace Realty, he is the owner and they specialize in rentals. His # is 312-519-6455 or firstname.lastname@example.org
Welcome to Chicago for the late summer!
PahRoo Appraisal & Consultancy
You are going to hear a bunch of nonsense on this board because most people are agents and want to direct you to places where they can earn money.
There are always sublets in Chicago, and generally a sublet is furnished because the person wants to return to their home. Winnemac Park is a very small area, so you should consider searches that include Lincoln Square, Andersonville, and Ravenswood. You will find the most studios in Edgewater, further east, closer to the red line. About a 20 minute walk or so to Winnemac park.
And August 15th sublet will be advertising now and will probably ask for August 1st. Try to negotiate to pay half the month rent, otherwise you'll have to suck it up and pay the whole month. Same goes for October.
Use Craigslist. Despite the amount of garbage currently on there, there is no better site for the variety of subleases. You can also post an ad on craigslist stating what you are looking for and budget. The sublease world is not run by agents. It's all done by individual renters. So...use caution. Make sure the person subletting to you is the true person on their lease AND...this is important, that they have permission to sublet. There are many landlords that don't allow this.
Remember...Chicago in the winter next time. It's the best!