Factual error: In a scene set in 1862 or 1863 Bill the Butcher says: 'An Irishman will do for a nickel what a ****** will do for a dime or a white man for a quarter'. The first nickel 5 cent piece was coined in 1866. At the time of the scene the 5 cent coin was a small silver coin called a half-dime.
Factual error: When Amsterdam kills the man that shot Bill the Butcher in the shoulder at the theater, you can see bananas on the floor. Bananas were traded in the U.S. only after the Civil War.
Continuity mistake: At several times during the movie, Butcher Bill's glass eye changes to what looks like a normal eye.
Continuity mistake: After Bill the Butcher stabs and beats Amsterdam's face badly (and brands him with a hot knife) notice how as time passes the wounds heal then reappear in varying degrees of severity. This is particularly true with the branding, which is almost absent by the end.
Factual error: When the Lords and posh folk are playing snooker they are using plastic tipped cues with blue chalk on the tip. These would not have been used in this time period.
Factual error: In one scene where Bill is in the Mayor's office, the mayor is sitting behind his desk and holding a bunch of papers, and on the upper right hand corner of the papers is a paper clip. Paperclips were not invented until 1899.
Continuity mistake: When Amsterdam arrives in New York City and is talking to his new friend, the bag he is holding switches from being held under his arm (camera shot from front) to being carried on his back (camera shot from the back). This happens at least four times in a row during the same scene.
Continuity mistake: After Jenny gets mugged at the dock, the shot shows her pulling herself to a standing position on a crate. In the next shot, from farther back and up high, she is crawling over to the crate she just pulled herself up on.
Other mistake: Towards the end of the movie, when the mobs are breaking into stores/houses, the police come to try and stop them. The mob starts to throw rocks at the police. You can see one of these rocks, which look like they should be heavy, bounce right off of one of the officers' heads, and just bounce around as it hits the ground, like it weighs nothing at all.
Other mistake: When Bill, Amsterdam and Tweed are standing on the docks, Bill mentions his father died in battle in 1814, 49 years before the movie takes place. Later, Bill tells Amsterdam that he's 47 years old. That means Bill's father died before he could have been conceived.
Continuity mistake: As someone pointed out earlier, the poster for the commemoration of the Five Points battle claims to be the 16th anniversary, but the date shows 1863 -- 17 years after the 1846 battle. To further add to the confusion, when William Cutting is talking to Amsterdam in the bedroom after the night at the brothel, he says, "I killed the last honorable man [Priest Vallon] 15 years ago [in the Five Points battle]." So which is it? 15, 16, or 17 years?
Revealing mistake: In the last scene where Amsterdam is crossing the black man's arms, wait until the camera pans onto Jenny. In the background there is another dead man and you can see him breathing pretty heavily.
Factual error: The prayer uttered at the beginning of the movie ("Saint Michael, the Archangel, defend us in battle; be our protection against the wickedness and snares of the devil") was composed by Pope Leo XIII in the year 1884. The movie is set during the American Civil War in the 1860's.
Continuity mistake: At the end of the fight in the bar between Amsterdam and Bill's Irish henchman, Amsterdam is in four consecutive shots from two angles bent over in pain, leaning back, doubled over again, and leaning back again as Bill approaches him.
Revealing mistake: The scene where Amsterdam and Jenny are in the room together above the tavern, shortly after Bill's assassination attempt, Amsterdam pushes Jenny up against a 12 inch by 12 inch wooden beam. The problem is when he is pushing her up against this beam, you can see it flexing with the weight. Then Amsterdam is holding the beam, you can see that the beam is some type of cloth because the slight touch of his hand makes it dent in.
Continuity mistake: When Amsterdam and Jenny continue talking after Bill has just left them in the bedroom, Jenny's hands keep shifting from both hands on her chest to just one hand between shots.
Revealing mistake: When Jenny gets mugged at the docks, a thug hits her in the stomach with a large wooden club. The club is obviously rubber, as it bends almost ninety degrees after hitting Jenny.
Continuity mistake: At their first encounter after Amsterdam's return to New York, Bill asks him to come closer. Amsterdam comes around the post he was leaning on, then the camera cuts to Priest Vallon's picture, and when Bill says it's close enough you see Amsterdam coming around the same post again.
Continuity mistake: When Amsterdam just met up with Jenny after she stole from the house, he is holding a handkerchief to his neck were he was cut. Then the camera view changes and his arm isn't there and it was too quick for him to move his arm.
Continuity mistake: The amount and position of the blood on Amsterdam's neck changes during the first fight with Jenny after he discovers she's a turtledove.
Continuity mistake: In the scene where Bill is cutting up the pig and is about to show Amsterdam the "kill" spots, he wraps up a piece of the pig for an old woman standing nearby. He throws the meat to Amsterdam to give to her and then reaches to unsheath a knife strapped to his right side. After Amsterdam gives the woman the meat and turns back around the shot cuts back to Bill and he is seen unsheathing the same knife he was holding seconds before.
Revealing mistake: In the scene where Bill has Amsterdam on the table, he begins headbutting him. You don't even have to look closely to see that Amsterdam's head is obviously just a dummy head with hair sewn on it. You can even see Bill headbutting it, and the head bends a significant amount, just like rubber. If it were Amsterdam's actual head his skull would be shattered in several places and he'd be killed instantly.
Continuity mistake: During the theater scene a man tries to murder Bill the Butcher but Amsterdam saves his life. As Amsterdam is wrestling with the culprit his hat falls off but in the next scene it's back on, then off again.
Revealing mistake: In the beginning of the Five Points battle it happens very often that people get hit badly with a sharp weapon but don't receive any wound. Watch for example in slow-motion how Bill sets out to mow down victim after victim with his cleaver. Later into the fight it becomes a lot bloodier, and sometimes the blood seems to come out of the weapon (e.g Monk's club seems to have a generous blood reservoir).
Revealing mistake: In the scene when Bill confronted Monk outside the barber shop, Monk invites Bill in to settle their score the democratic way. As Monk led the way, Bill threw his big butcher knife into Monk's back. The knife can be seen bouncing off Monk's back onto the ground.
Continuity mistake: When Amsterdam tries to kill the butcher and fails, the butcher straddles Amsterdam on a table and tosses a cleaver in the air. The cleaver rotates counter-clockwise so that the blade is rotating backward; however, when the cleaver lands, it is rotating clockwise so that the blade sticks into the wooden table. This would be impossible the way the cleaver is tossed into the air with a back-handed flip.
Continuity mistake: Jenny pokes Amsterdam with her knife on the right side of the neck as he is trying to retrieve his medallion from her. Shortly afterwards, while walking back with her, he is seen dabbing the left side of his neck in two different shots, one of them pretty lengthy.
Revealing mistake: In the first fight scene, Priest Vallon stabs a man from behind with his sword. You see the sword go under his arm where he holds it there.