This is the county's first case this year and the second for Illinois.
The DeKalb County Health Department said people may have been exposed at the following locations and times:
Anyone who has been exposed and is not vaccinated should monitor themselves for symptoms the next few weeks.
SEE ALSO | Map shows how to spot the measles risk level in your ZIP code
Symptoms of measles may include a rash, high fever, cough, runny nose and red and watery eyes.
Anybody who was exposed and developed a rash, and another one of these symptoms, should contact the health department.