The child was apparently attempting to cross the road while playing with friends and family members when he was hit.
Lucus Polhemus died at Johnson City Medical Center on Saturday.
Polhemus was struck by a 1985 GMC pickup truck driven by William D. Boehm, who was topping the crest of a hill when the boy suddenly came into his view, police said.
Investigators with the Tennessee High Patrol determined there was nothing Boehm could do to avoid the accident. Speed was not a factor.