The Swearingen Funeral Home says Harjo died March 31 at Mercy Hospital in Ada Harjo's nephew, Richard Harjo, says his uncle had a heart attack.
Harjo was a member of the Seminole Nation of Oklahoma. He was also one of the last surviving members of a group of American Indians who used their native languages to outwit the enemy and protect US battlefield communications during World Wars I and II.
Harjo traveled to Washington DC last November to take part in a ceremony where congressional leaders bestowed the Congressional Gold Medal, its highest civilian honor, on American Indian code talkers.