The sheriff's office said authorities responded to the crash in the 5200-block of Lake Street in unincorporated McHenry just before 10 a.m.
A 2018 Toyota Highlander struck the child, who was riding a Razor MX350 dirt bike, in the intersection of North Lake Street and West Pleasant View Drive, the sheriff's office said.
The sheriff's office said LifeNet flew the child to Loyola Medical Center with life-threatening injuries. The child remained in critical condition on Friday.
The driver of the Highlander declined medical attention, the sheriff's office said. That driver was issued a citation for not driving on right side of a two-lane road.
The McHenry County Major Crash Investigation Unit and the Department of Children and Family Services are investigating, and additional charges are possible.