Police and firefighters rushed to Millennium Park last Saturday where a suspicious package was found. It had batteries and wires and was near the popular Cloud Gate sculpture, known as the Bean.
The park was evacuated before bomb and arson officers determined the package wasn't dangerous.
Chicago's law department says the city usually tries to recover its expenses in such cases.
An 18-year-old suspect was charged with disorderly conduct. The city is adding up what the hoax cost and may sue the man.