The Cary Fire Protection District responded to the 28700-block of West Kristy Lane around 12:40 p.m.
There, paramedics found a young child who had been run over by an industrial-style lawnmower. A neighbor had applied a makeshift tourniquet to the child, who suffered a serious leg injury.
The child was transported to the Mercyhealth Hospital - Crystal Lake helipad, where a medical helicopter was waiting. He was then airlifted to Loyola University Medical Center in Maywood in critical condition.
The Lake County Sheriff's Office is investigating. Further information was not immediately available.