Colin Farrell and the other cast members had to spend six weeks at a ranch, hanging out with cowboys, and learning how to ride horses before filming began. Farrell rode a horse named Milagro, and used that horse while shooting the film.
In the credits it is mentioned the use of footage from the movie Maverick (1994). It is the short scene of the paddle wheel steamer when Jesse (Colin Farrell) and Zee (Ali Larter) are getting to Florida.
The trivia items below may give away important plot points.
In the film, Frank and Jesse's mother is killed by an explosion, when the Agents raided the James homestead. While the explosion did take place, their mother lived, but had her arm blown off, and a younger half-brother (omitted from the story) was killed.