Revealing mistake: Although the film is set during the aftermath of the Mexican War (1848-50), the mountain vistas display some lovely radio towers and fire ranger stations.
Continuity mistake: Jeremiah finds Hatchet Jack frozen to a tree and begins to approach him. In every close-up shot of Hatchet Jack, you can see Jeremiah's rifle resting on the tree behind him. The rifle is then absent during shots from further away as Jeremiah approaches. Jeremiah does not place his rifle there until he reaches Hatchet Jack and begins reading his note.
Continuity mistake: Jeremiah Johnson acquires two horses at the beginning of the movie, one completely black, and one almost completely brown. A few minutes later, Jeremiah Johnson is seen riding a horse that is different than the two he just acquired. The new horse is distinguished by his near entirely white face.