Factual error: When Rachel and Samuel are at the 30th Street Station in Philadelphia, the door Samuel walks through is not (and never was) the men's room entrance. The men's restroom is further to the left, behind the wall and out of the camera view. Also, the men's room at the 30th Station was never that dingy looking and, at that time of day, would have had a very steady flow of patrons going in and out.
Revealing mistake: After Book shoots McFee, McFee is leaning against the wall with a shotgun in his hand. He is holding a full pump action shotgun with one hand pointed up while wounded and then fires the gun. When he does, there is absolutely no kick to the shotgun at all, revealing it to be a blank shot.
Deliberate mistake: To keep things simple, the movie relies on the Lancaster County Sheriff as a county police force. In reality, the county sheriff serves the county court (transporting prisoners, for example) but does not serve as a county wide police force. In PA, each city, borough, and township has its own police force. Note the varied colors of police cars at the farm in one of the final scenes. These were borrowed from the various local police forces (Lancaster City, for example, is robin egg blue with a white top).
Character mistake: Locals pronounce Lancaster as LANGkaster. It is commonly mispronounced "Lankaster." When Shaeffer first calls the local police, the sergeant first pronounces Lancaster correctly but incorrectly later in the call.
Continuity mistake: When the local bums provoke the Amish, Viggo Mortensen's hat is grabbed twice - for the first time when the leader of the gang smears Alexander Godunov's face with ice cream, the curly-haired guy can be seen swiftly grabbing Mortensen's hat in the background. Thereafter Mortensen is hatless - until the same curly-headed bum grabs his hat again, now in the wide shot. (01:25:05)