Other mistake: When Mattie is going to get water from the creek, she is shown carrying a large, bulky, heavy wooden bucket. Had they been carrying this in their gear, it would have been visible, but this bucket is never seen among their equipment prior to this scene. Not to mention, it would have made much more sense to have used a canvas, collapsible bucket as they used in the original film.
Continuity mistake: When Mattie crossed the river on horseback, she was submerged to her chin. When she exits the water on her horse, her clothes, gear, boots and hair braids should have dripping wet. They appeared dry. When the ranger pulled her off her horse onto the ground, her wet clothes would have caused the dry dirt to cake on her like mud.
Continuity mistake: In the first shot of the dead man hanging form the tree, his head appears to be about 12" from the tree limb. After Mattie climbs up to cut him down, his head is several feet from the tree limb.
Factual error: The opening sequence has trains passing opening to the town scene. The trains are passing over a modern (1990) railroad crossing.
Factual error: The epilogue dates the main story as having taken place in the 1870s. In the opening scene, the locomotive tender has distinctive cast Bettendorf trucks (bogies) which were not introduced until c. 1900.
Continuity mistake: During the scene where Matt Damon is sitting at the edge of the bed where Hailee Steinfeld is sleeping, he sets his pipe down and the smoke from the pipe disappears and reappears in a different place right after he says "A saucy line will not get you far with me."
Factual error: The story takes place in 1875, but Rooster's Colt Army revolver has a cylinder cross-pin in the frame that did not appear on Colts until 1896.
Character mistake: Mattie attended a travelling Old West show in Memphis in which Rooster Cogburn was a performer. The flyer for the show shows the date of the show as July 18, 1903. The day of the show Mattie was told that Rooster died three days earlier (July 15, 1903). But Rooster's tombstone lists the date of his death as August 12, 1903.
Factual error: The mine that Rooster fires his pistol into is shown to go far into the hillside. A lot of digging has occurred here. However, the exterior shot of the mine shows no mine tailings whatsoever. There should have been a substantial amount of removed rock outside the entrance.
Factual error: The soles of the boots worn by Rooster are incorrect for the period. They are not smooth, but are patterned for mountain climbing. The soles of the boots may be seen in the scene in which Rooster is drunk and challenges the Ranger in target shooting.
Continuity mistake: There is a scene where it is pouring rain and they are all huddling under a tarp hung between trees. when they start to walk around afterwards, the ground is completely dry; no mud.
Audio problem: During the second camp fire scene at night (after the trio have looked in the cave/railway) Mattie finishes talking but in a wide angle shot the character can still be seen moving her mouth but now without any sound.
Continuity mistake: In the ending long profile shot of old Mattie, the tree, and the tombstones, you can see that they are standing on a hill. In the following shot, you see the back of old Mattie walking away from the tombstones. The top of her head stays at a constant height while she walks quite a long distance. This would not be the case if she were working down a hill - her head would slowly get closer to the bottom of the screen.
Continuity mistake: When Mattie is trying to catch up with Jeff Bridges and Matt Damon when they initially leave town without her, she comes to the river and sees them more than 100 yards on from the river. She then drives her horse through the river and they stop and watch her. When she exits the river they're right on the river bank although they did not move throughout the scene.