Parents of students at Evanston Township High School were warned Monday to ensure their child's vaccinations are up to date.
In a notice posted to the school's website, officials said someone in the school "may have contracted a case of mumps." The notice did not identify if the person was a student or staffer at the school.
Through the end of April, 82 cases of the viral infection were reported in Illinois. That's more than triple what was reported in all of last year. The Illinois Department of Public Health said this year's total is already the highest since 2008 when 91 cases were reported.
Authorities don't know what's behind the spike.
Last month, health officials reported an increase in cases of the viral infection in Morgan and Sangamon counties in central Illinois.
Mumps can cause swelling of the salivary glands, along with fever, headaches, muscle aches, tiredness and loss of appetite.
Eight students at a college campus in New Jersey were diagnosed last month with the disease. Some of the Stevens Institute of Technology students lived in the same fraternity house and some were members of the lacrosse team, according to other students on campus.
The Associated Press contributed to this report.