John Dillinger's lawyer at Crown Point, Louis Piquett, never went to law school. He passed the bar on his fourth attempt, receiving his license to practice in 1920.
In the commentary, Michael Mann reports that a crew member pointed out that the date was April 22nd. Mann then realized that they were filming on the anniversary of the actual shoot-out of the Little Bohemia lodge.
While filming on location in Oshkosh, Wisconsin, a boy, aged eleven, told Johnny Depp he loved his Fedora hat and would like to have one like it. Depp told the boy he would see what he could do about that. After filming finished, Depp sent the boy the hat in the mail.
For John Dillinger's famous escape from Crown Point Jail, the film makers decided to film at the real jail, which had been closed and turned into a historical museum when the new jail opened in the 70s. They dressed the jail and store fronts on the square to its original condition, as it would've appeared in 1933. They also filmed the Little Bohemia shoot-out at the real lodge. Johnny Depp was staying in the same room the real Dillinger stayed in.
During a robbery, Dillinger says to a bank customer "We're here for the bank's money, not yours." It's similar to an exchange between Clyde Barrow and a farmer during a bank robbery in Bonnie und Clyde (1967), "Is that your money or the bank's?", "It's mine.", "You keep it then." There is some dispute over which real-life bank robber spoke this line. Supposedly, John Dillinger said it to a bank customer while robbing a bank in Greencastle, Indiana. However, some historians attribute the line to Charles Arthur "Pretty Boy" Floyd. Most historians agree that Clyde Barrow never used the line. This scene is also similar to the bank scene in Heat (1995), when Robert De Niro's character states, "We're here for the bank's money, not yours."