Revealing mistake: When Stevens leaves the house about halfway through and sits on a bench there is a modern electrical outlet on the wall to his left.
Factual error: In one of the scenes in which took place in a white room, on the door behind the character's head is a modern day "door closer". Door closers were invented in 1880 by Lewis C Norton of the the LCN Company and the first one was installed at Boston Trinity Church in 1880, was some 15 years after this film took place.
Factual error: In the flag ceremony Lincoln raise a US Flag with 35 stars which was in use from 1863-1865. Later, Lincoln is riding through the aftermath of a battle scene and the soldier following is carrying a flag which matches the 1877 US flag with 38 stars.
Continuity mistake: In the scene where Tommy Lee Jones takes home a copy of the bill it is folded lengthwise, when he hands it to Epatha Merkeson it is folded crosswise.