Director Jon Favreau was constantly harassed with demands to shoot or convert the film in 3-D, but he held his ground, claiming Westerns should only be shot on film.

Daniel Craig was chosen because of his distinct likeness to Steve McQueen, who starred in the cowboy epic The Magnificent Seven (1960).

Daniel Craig recommended Eva Green for the role of Ella after working with her in Casino Royale (2006). However, Eva turned the role down and Olivia Wilde, who'd auditioned for Eva's Bond role of Vesper Lynd, was cast.

Robert Downey Jr. was set to play Zeke Jackson (a "former Union army gunslinger"), but dropped out, due to scheduling conflicts. Within a month, the character was re-named Jake Lonergan, re-written to be an outlaw, and Downey, Jr. was replaced with Daniel Craig.

The filmmakers cite Alien (1979) and Predator (1987) as an influence on the look of the aliens in the film.

Harrison Ford wanted to go bareheaded in the film and not wear a hat (he is most famous for his performance in the Indiana Jones film franchise, where he wore a fedora), but since it was a Western, he was convinced to wear a hat. In American Graffiti (1973), Harrison Ford was asked to cut his hair (to go bareheaded with a period haircut) for the film. He refused, stating that his role was too short, and offered to wear a hat instead.

The fabric used to make Ella Swenson's dress had originally been considered for Hailee Steinfeld's wardrobe in True Grit (2010), but had been deemed too feminine for that movie.

This is DreamWorks' third comic book adaptation, after Road to Perdition (2002) and Over the Hedge (2006).

DIRECTOR CAMEO (Jon Favreau): (At around nineteen minutes) His mugshot can be seen as the Sheriff notices, and takes off the wanted poster of Jake Lonergan.

Steven Spielberg screened The Searchers (1956) and Close Encounters of the Third Kind (1977) for Roberto Orci and Jon Favreau so that they could get the atmosphere of the film.

Director Jon Favreau starred in The Big Empty (2003). In one of the last lines of that film, Kelsey Grammer dismisses Favreau's account of the events that had occurred as a tale "of cowboys and aliens."

As with most films distributed by Universal Pictures, there is a brief promo after the end credits for Universal Studios. However, the promo used at the end of this movie uses the decidedly 1960s-era ad to promote the Universal Studios back lot tour in Hollywood, California. This promo was replaced in 1990, when Universal Studios opened a second location in Orlando, Florida, and changed its logo.

The film had been in development hell for over a decade, with it's original idea conception dating back to 1997. The film was pushed back for years, and several big named actors were attached to the project at one point, such as Jackie Chan, Robert Downey Jr., Brendan Fraser, Chuck Norris, Kurt Russell, Mr. T and Bruce Willis, before dropping out and being replaced. Directors Joe Johnston, Steve Oedekerk, and Ron Underwood, as well as several others, were also attached to the project at one point in time.

With this film, Harrison Ford has shared the screen with the first and latest actors who have played the James Bond role: Daniel Craig in this film, and Sir Sean Connery in Indiana Jones and the Last Crusade (1989).

Screenwriters Roberto Orci and Alex Kurtzman described the film as "Unforgiven (1992) with aliens landing."

Steve Oedekerk was originally set to write and direct the film, but dropped out. He received a story credit for the final film.

An early draft of the screenplay was written by Thomas Dean Donnelly and Joshua Oppenheimer.

Harrison Ford and Olivia Wilde are the only ones in the cast to wear a Six Gun holster for rapid draw, in the front w/the gun not on the side like so many movies showing Cowboys on the side draw

Daniel Craig and Harrison Ford went on to star in Star Wars: The Force Awakens (2015). Harrison Ford reprises his role as Han Solo, and Daniel Craig portrayed a Stormtrooper.

East of Jal, NM, is the Dollarhyde Oil Lease which borders Eastern New Mexico and West Texas.

In the final scene of the movie, a "Southland Ice Company" ice wagon is shown. Southland Ice Company is the predecessor company to 7-11 stores.

Body count: thirty-four.