There are an additional seven probable cases and 20 suspect cases at two high schools, two middle schools and the surrounding area, health officials said.
But county health officials continue to field reports of probable and suspected cases since first reporting a confirmed mumps case in Barrington High School on February 28.
A case of the mumps has been confirmed at O'Connell Drive Elementary School in Porters Lake, N.S.
In a newsletter, school officials assured parents that they shouldn't feel overly concerned about the case. There is also one suspected case in Cook County, in Arlington Heights.
Victor Plotkin, an epidemiologist with the Lake County Health Department, said health officials usually decide to confirm a mumps case when a particular case has a positive viral test showing symptoms of mumps. The mumps diagnosis by the city's Department of Public Health is only preliminary, and CPS says it will work with the department to take whatever precautionary measures it needs to, the report added.
Schools affected have been undergoing deep cleaning.
The mumps virus is spread when a person with the illness coughs or sneezes nearby, or shares food or drinks with other people.
"If you are not feeling well, stay home", McWilliams said to students and faculty.
Symptoms of mumps are fever, headache, muscle aches, tiredness and loss of appetite plus swollen glands and swelling or pain close to the jaw or on both sides of the face.
Chicago Public Schools notified parents on Monday about a case of mumps at Helen C. Peirce School of International Studies, 1423 W. Bryn Mawr Ave., according to the district.