buenos dÃas Agustin,
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