The (Springfield) State Journal-Register says the cases of cyclosporiasis have been found in Jo Daviess, Sangamon, Montgomery and Lake counties.
The infection causes prolonged watery diarrhea and sometimes explosive bowel movements, weight loss, cramps and fatigue, among other symptoms.
The parasite has sickened more than 350 people in 15 states as part of the most recent outbreak, which the public health officials believe is connected to imported fruits or vegetables.
Melaney Arnold is a spokesman for the Illinois Department of Public Health.
She says none of the Illinois cases required hospitalization.
Authorities are trying to see if the cases are connected to the nationwide outbreak.
