An autopsy shows Jacob Lord died of an inflicted closed head injury.
Indiana State Police say the child's mother first took the boy to the hospital in Scottsburg, but doctors quickly had him transferred to Louisville.
He died yesterday at Kosair Children's hospital.
"We've been working on this thing non stop since we got it yesterday. Our detectives have not been home not been to bed and we're going to stay here until we get this resolved," said Sgt. Jerry Goodin, Indiana State Police.
Police aren't releasing any other details on the child's injuries and no arrests have been made.