State representative Jack Franks says "Caylee's Law" closes a loophole in Illinois' law.
The law comes after two-year-old Caylee Anthony, from Florida, was found dead months after she went missing.
Her mother, Casey Anthony, waited a full month before reporting her missing.
Casey was eventually convicted for lying about the circumstances surrounding the child's disappearance and death.
Caylee's Law makes it a Class 4 felony for failing to report a child missing in the allotted time.
The crime is punishable by one to three years in prison and a fine of up to 25-thousand dollars.