You have a single family residence, that's why the zoning cert states "one." If you want to rent a room on the second floor, that's probably OK. If you want to rent the second floor as an apartment, that's not going to be OK. If you want to change the zoning of your property to accommodate more units, consult a real estate attorney. It may be possible to do so, but you will have to make changes to your house to make it legal.
Attorney Ranj Mohip is a Chicago real estate attorney. The information in this answer is general information and is not intended as legal advice. Further, answering this question or otherwise contributing as a member of Trulia.com does not create an attorney-client relationship. Remember--consult the best real estate attorney in Chicago or in your respective area. Contact us at http://www.ranjmohip.com for more information.