On Saturday, the state health department announced it is investigating its first "probable" case.
The case surrounds an unidentified Chicago resident, who officials say is experiencing symptoms of meningitis.
The person received an epidural injection of a possibly tainted steroid medication. Further testing and treatment is underway to see if the case is linked to the national outbreak.
A federal investigation found possible fungal contamination of steroids that a Massachusetts company shipped nationwide.
At least two Chicago locations received a shipment. One of them is where the sickened Illinois resident got their injection.
So far, nearly 200 meningitis cases have been reported in 13 states. The outbreak has killed 15 people.