Factual error: When Wyatt (Kevin Costner) becomes the sheriff/deputy/policeman of Wichita, Kansas, you can plainly see mountains in the background - there aren't any around there.
Factual error: In the opening shot of the film, a big oak door opens - carved in it is the date 1862 - 42 years after George III died.
Factual error: The movie is set in the late 1950s, yet Ed's car has yellow-on-black California license plates that weren't issued until 1963. The plates on Ed's car should be black-on-yellow 1956 issue plates.
Factual error: What on earth is the conductor at the premiere of the 9th doing with a baton? This was not used until around 1849, and the premiere of the 9th is in 1824.
Factual error: In the film, John Lennon sings "Long Tall Sally" when it was actually Paul McCartney who sang/recorded the song.
Factual error: A carton of HEB milk is taken out of the fridge and it has the new (as of 1994) label on it. The movie is set in the late 80s, when the old style label was still used.
Factual error: In one scene Cobb and the sportswriter doing his biography are driving across the country to get to the baseball Hall of Fame. They are stopped next to some railroad tracks fixing a flat tire, and a train goes by that has Burlington Northern markings (BN). Burlington Northern didn't come into existance until ten years or so after Mr. Cobb died.