In a newsletter, school officials assured parents that they shouldn't feel overly concerned about the case.
The Chicago Department of Public Health is investigating a potential case of mumps at Peirce Elementary School, according to CPS.
Three confirmed cases have been identified at Barrington High School, and a fourth unrelated case has been confirmed in Barrington, but that person has no connection to the school.
The additional cases come a day after Toronto Public Health confirmed that three cases in the outbreak are from three different local schools. There is also one probable case of the mumps at a school in Arlington Heights in Cook County.
Despite the three cases found, one in each of three schools, Dr. Vinita Dubey, an associate medical officer with Toronto Public Health, said the virus has mainly affected 18-to-35 year olds who frequented bars in part of the city's west end.
"We've done some thorough cleaning of our facilities, especially over the weekend when no one was in the building, we were cleaning with a bleach based solution and focusing on the high touch areas like door knobs, bathrooms tables and chairs", said Morgan Delack of Barrington School District 220.
The school notified parents of the confirmed cases and officials stressed this is a "cluster" of mumps and not an outbreak.
In severe cases, mumps can cause infection in the brain, painful swelling of the testicles or ovaries, pancreatitis and hearing loss.
"If you are not feeling well, stay home", McWilliams said to students and faculty.