Prior to production, United Artists had made it clear to director John Sturges that none of the primary roles were to be filled by actors who had played the same characters in Règlements de comptes à O.K. Corral (1957). Sturges believed that the roles of Virgil and Morgan Earp from the previous film were small enough that the same actors could do it again without harming the film's uniqueness. The studio agreed, and allowed Sturges to cast John Hudson and DeForest Kelley. Hudson had retired from acting in the early 1960s, and was unwilling to come back. Kelley was working on Star Trek (1966) and unable to break away. Thus, both Earp brothers were re-cast.
The movie depicts Tombstone to have a railroad with depot. The railroad did not come to Tombstone until 1903.
Wyatt Earp's giving Warshaw a chance to draw against him is taken from the story of Earp doing that with Florentino Cruz, who also said he'd been paid $50 for his participation in the assassination of Morgan Earp, according to the Stuart N. Lake book "Wyatt Earp: Frontier Marshal." However, in the movie, Earp empties six shots into Warshaw. The real Wyatt Earp kept only five rounds in his pistol, resting the hammer on an empty chamber for safety, according to the Lake book.
The historical "Vendetta Ride" on which this film is based was in fact a murderous rampage carried out with no legal authority. Previously, Wyatt Earp had relied on the legal system to bring the Cowboys to justice, but after the suspect in his brother's murder were freed, he decided to take matters into his own hands. He held the office of US Marshal at the time to enable the arrest of the Cowboys, but warrants were issued against him and his deputies for extra-judicial murder. In 1882 Pima County Sheriff Bob Paul rode to Colorado to extradite Wyatt, Warren and Doc back to Arizona. He served the warrant to a dying Doc, but not to the Earps with whom he was friendly. Later the same month Colorado Gov. Pitkin refused to honor Arizona's extradition request, allowing Earp and the others to leave the state.
Sheriff Jimmy Bryan is based on the notoriously corrupt County Sheriff John 'Johnny' Behan, a former lover of Wyatt's future wife Josephine Marcus (Josie). The reason for the name change is unclear.