To become an RN, you atleast would need an Associates Degree. This takes about 2-3 years to complete. Many of the City Colleges of Chicago offer an associates degree in nursing I believe. It is very competitive though, and I hear the waiting lists are very long.
I personally went to Saint Xavier University on the south side of Chicago. I just graduated. It is a 4 year program that offers a Bachelors of Science in Nursing.