The Chicago Tribune reports a forensic anthropologist determined the skulls are real, but just anatomical models like the kind used in classrooms and or a doctor's office.
A boy found one near his home in a rural area of Bull Valley. Investigators found the second one nearby.
McHenry County Coroner Marlene Lantz says the skulls were so white that they appeared bleached by the elements. But she says that apparently was a result of them being prepared for display.
The Associated Press contributed to this report.