Illinois is the "Land of Lincoln" and that means that Abe's birthday is celebrated as a state holiday.
Monday, February 12th, expect most city, county and state offices to be closed. That includes most courts, all Chicago Public Libraries, aldermanic offices, City Hall, City Clerk's offices, Secretary of State's office, etc.
Chicago Public Schools will be open.
Most banks will be open, and there will be mail delivery.
Next Monday is Presidents Day, so expect the same then, with federal offices closed as well.