Errors in geography: A mountain range is seen looming over Plainfield, Wisconsin, which as its name suggests, is on a plain.
Anachronisms: A gas pump says "5% sales tax added." The movie takes place primarily in 1957; Wisconsin did not have a sales tax until 1962, when it was 3%. The sales tax did not reach 5% until 1982.
Factual errors: Both Ed's mother and, later, Ed himself read passages from the book of Revelations in the Bible (primarily focused on the 'whore of Babylon')... but they are reading from about the first 10% of the book, while Revelations is the very last part of the book.
Anachronisms: After Ed kidnaps the bartender, he takes her home in his truck. on the way home they pass a vehicle traveling in the opposite direction. the vehicle has rectangular headlight. this type of headlight was not found on vehicles in the '50s.
Continuity: We can see that the cash register at the local store reads $2.22 before Gein's purchase is rung up. When we hear the distinct sound of the cash reel mechanisms, the clerk tells Ed "that'll be $2.22" even though nothing moved. A few days later Ed steals the cash register and puts it in the back of a delivery truck, and the readout still shows $2.22. Clearly a non-working cash register that the producers tried to get too much mileage out of.
Crew or equipment visible: Actors in several scenes can be seen breathing while they are lying prone, even though their characters are supposed to be dead.
Miscellaneous: Ed Gein, and most of the other characters in the movie, speak with southern accents, but Ed Gein was from Wisconsin, and the film takes place there.
Factual errors: The real owner of the hardware store in Plainfield was Bernice Worden. There is no known evidence of anyone named Collette Marshall having anything to do with the Ed Gein incidents.
Factual errors: Although Gein has often been referred to as having been a cannibal, he never confessed to such nor was any evidence of actual cannibalism ever found.