Director Clint Eastwood dedicated the film to directors and mentors Sergio Leone and Don Siegel. The final screen credit reads, "Dedicated to Sergio and Don."
Clint Eastwood's mother Ruth Wood toiled through an uncomfortable day (wearing a heavy dress) as an extra, filming a scene where she boards a train. However, the scene was eventually cut, with her son apologizing that the movie was "too long and something had to go." All was forgiven when he brought her to the Academy Awards and thanked her prominently in his acceptance speech.
The script floated around Hollywood for almost 20 years. Gene Hackman read and rejected it, only to be later convinced by Clint Eastwood (who had owned the rights for some time) to play a role.
Shot near Calgary, Canada, which was experiencing unusually dry weather. Most of the rain was created on-site. The snow that falls when William Munny is recovering from his beating was unexpected and unscripted.