This marks the second case in the county in 2025, according to the Cook County Department of Public Health.
CCDPH said a 4-year-old, who is not vaccinated, tested positive.
Officials believe the child might have contracted measles during international travel.
The public might have been exposed on Thursday, September 11 at O'Hare International Airport, at terminal 5 between the hours of about 7:30 a.m. and 11 a.m.