Continuity mistake: When the mother and son are shot, it shows from the outside, and the gunfire flashes in the one (suspected) bathroom where they were killed. Just before, the light was on, and then when Jr. went to find them, the light was back on.
Factual error: Tom Hanks with his son pulls into the small town, parks diagonally at the curb, tells his son to stay in the car and honk if he sees trouble. He walks to a building, the curb of which at the corner is shallowed to street level for handicap access. Handicap curbs are a modern development, certainly not around in the 1930s.
Continuity mistake: During Sullivan and Maguire's gun fight at the hotel, between the fifth and sixth shot Maguire takes at Sullivan, a bullet imprint instantly appears on the trunk Sullivan is taking cover behind, in the top right corner.
Continuity mistake: When Michael Jr. is doing his math homework, he holds his pen between his forefinger and middle-finger. In the next camera view, the pen is between his middle-finger and ring-finger. The books are also in different positions. When camera switches back to the first view, everything is as at the beginning again. (00:04:35)