Sheriff's Capt. Trace Frost said Ilan Hurtado died Tuesday from injuries sustained in the Aug. 15 crash in the Town of Beaver Dam.
The boy from Lindenhurst, Illinois, was in a car driven by a 45-year-old woman also from Lindenhurst. The sheriff's department says she was driving on a highway and slowed down to turn. A semitrailer hit her car from behind, sending it into the northbound lane. The car struck a van driven by a 31-year-old woman.
Hurtado was flown to a hospital. The car and van drivers were hospitalized with non-life-threatening injuries. The semitrailer driver wasn't injured.
The sheriff's office didn't say whether charges have been filed.