Sumter County Coroner Harvin Bullock said Tommy Tindal died at 3:35 p.m. Saturday of massive head injuries and multiple trauma.
The South Carolina Highway Patrol said Tindal was not wearing a helmet.
Tindal was riding his bike southbound on the northbound shoulder of S.C. Highway 441 when he was struck by the box truck driven by 64-year-old Robert Reynolds of Chapin. Reynolds was not hurt.
Authorities are investigating the accident.