Robert Duvall based Jackson Fentry's unusual accent on a man he met once while walking the foothills of the Ozark Mountains. Duvall was so struck by the man's deep-voiced accent, he never forgot it.
According to later interviews with Robert Duvall and Writer Horton Foote, they had real difficulties working with Olga Bellin, who insisted on doing scenes entirely her way, and not listening to Director Joseph Anthony. Duvall and Foote vowed never to work with her again. Filmatically, this wouldn't have been a problem, as Bellin confined her work to the stage, and never made another film. She died of cancer in 1987.
In William Faulkner's original short story, Sarah was ""black complected", which means she had dark hair, not dark skin.
The late, great comedian Norm MacDonald revealed in an interview with Robert Duvall that this and Tendre bonheur (1983) were two of his favorite films.