In February, Stephon Watts' family members called police to their home in Calumet City because the teen was acting out.
Watts was diagnosed with Asperger's syndrome.
Police contend they shot him after the teen lunged at an officer with a knife.
Early reports indicated the weapon was a butter knife, but an investigation determined it was a steak knife.
A review by the Cook County state's attorney concluded that the conduct of the officers involved in the shooting did not warrant criminal charges.