Factual error: Tom Hanks is driving his car over a bridge in downtown Chicago in 1931. In the background is the elevated train structure. An aluminum bodied train passes on the trestel in the background. This aluminum bodied train is of 1980's contruction. In the 1930's the train cars were of wood construction and painted brown. They were still in service in the 1950's.
Revealing mistake: At the end when Sullivan is shot in the back while looking out the window, you can see blood come through the front of his shirt, meaning the bullets must have exited his body, yet the window he is standing in front of isn't shattered by the bullets that had passed through him. Also, immediately after this when Jude Law sets up his camera to take photos of Tom Hanks dying, the blood all over the glass is completely gone. The window is clean.
Continuity mistake: In the end of the diner scene Jude Law fires after the car with Sullivan and his son. A bullet goes through the rear window but not through the windshield. We see the bullet path go by Tom Hanks' head. Regardless, there's no bullet hole anywhere in the car afterwards.
Factual error: In the scene when Mike Sullivan is shown sitting in his classroom, the American Flag behind him has 50 stars, which it wouldn't have in the 30's.
Factual error: If the movie is set during 6 weeks of winter in 1931, then why do we hear the sound of crickets during a couple of night scenes?
Continuity mistake: When the young Sullivan boy goes to get Rooney's over coat, he walks into the room where the coat is and there is a man laying on the couch, if you notice when the man starts talking to the boy, his cigarette is almost gone, and in the next few seconds it flashes to the man again and he has a cigarette that is almost full. (00:09:20)
Continuity mistake: When Sullivan and his son are robbing banks, there are several shots where you can see four or five getaway scenes. If you look closely, you can see them making a getaway from the exact same scene twice.
Factual error: The second original old song is "Queer Nations" performed by Fletcher Henderson, but this song was recorded in 1934, not '31.
Continuity mistake: In the scene where Tom Hanks is battling Jude Law in the hotel room, just before you see Hanks shoot the glass vase that shatters in Law's face, there is a shot of Tom Hanks jumping out behind the chest to get the final round off. Unfortunately, Tom Hanks's 1911 is empty in that shot - you can see the slide locked back.
Revealing mistake: Towards the end of the scene where Connor shoots the wife and younger brother, he looks at his reflection in the glass at the front door. In the shot of Connor walking through that door onto the porch outside, you can see the icicles hanging from the gutter over the porch actually swinging. (00:40:00)
Continuity mistake: In the scene where Paul Newman's character hands Michael, Jr. a silver dollar, the first camera angle (from Michael's perspective) shows the "heads" side presented toward the kid. The next angle (from the opposite point of view) also shows the dollar with the "heads" side toward the camera, which means the "tails" side (an eagle) is what the kid should have seen.
Continuity mistake: Look carefully at the Lone Ranger book that Michael Jr. is reading at two points in the movie (once when he's reading in his bed as he and his brother are talking about their dad, and again in the car after his mother and brother are killed.) The picture and caption under it are identical, but the text on the facing page is different each time.
Audio problem: In the scene where Michael Sullivan robs his first bank before the montage and is in the manager's office, Michael offers him a little present. Sullivan says, "Call it a handling charge," and the camera is focused on the manager, but the words aren't matching what Michael Sullivan is mouthing.