Apr 1939 HR news items reported that Union Pacific's world premiere in Omaha, Nebraska was a gala "three-day celebration" that drew crowds of over 250,000, instantly doubling the city's population and requiring the deployment of eight national guard troops to help local authorities maintain order. Large crowds were also said to have gathered at many stops along the train route from Hollywood to Omaha, as it was publicized that a special train carrying, among others, producer and director Cecil B. De Mille, and stars Barbara Stanwyck and Joel McCrea, was making its way to Nebraska for the event. The film's premiere took place at three Omaha theaters simultaneously. A 22 Apr 1939 HR news item noted that President Franklin Delano Roosevelt was to officially start the premiere proceedings by pressing a button in Washington, D.C. that would open Omaha's civic auditorium. An advertisement in HR claimed that Union Pacific's premiere, which was accompanied by parades, special radio broadcasts and a banquet, was the "biggest world premiere in motion picture history." The ad also notes that following the premiere, De Mille was joined by many of the film's stars aboard an antique train for the continuation of the fifteen-day, coast-to-coast promotional tour, which was scheduled to stop at thirty cities around the country.
       According to material contained in the Paramount Story Files at the AMPAS Library, a treatment dated 31 May 1938 was written by Frederick Hazlitt Brennan for actors Fredric March, Joel McCrea and Irene Dunne. HR pre-release news items and early production charts indicate that actor Charles Bickford was originally cast in the role played by Brian Donlevy. According to HR, when Bickford "stepped out of the part because he didn't like it," he was replaced by J. Carrol Naish, who could not appear in the film due to a scheduling conflict with his assignment on Paramount's Federal Offense (see above). Although a HR pre-production news item announced that actor Porter Hall had been signed for a feature role as the engineer, he did not appear in the released film. Modern sources indicate that De Mille's first choice for the female lead was Jean Arthur, and that Lynne Overman took over the role previously assigned to Bob Burns and Walter Brennan.
       According to a pre-release HR news item, De Mille directed the film from a stretcher because he was recuperating from an operation he underwent months earlier. Studio records, however, report that De Mille was confined to a stretcher for two weeks following his collapse, which was said to have resulted from the strain of directing three units on the film simultaneously. A 12 Dec 1938 HR news item notes that while a third unit was put to work under director James Hogan, second unit director Arthur Rosson was filming in Cache, Oklahoma. A 27 Dec HR news item indicates that Rosson's second unit was dispatched to the Mojave Desert, California for location shooting.
       Other shooting locations noted in contemporary sources were Canoga Park, Stockton and Sonora, California and Cedar City and Iron Springs, Utah. Studio publicity material claims that one hundred Navajo Indians were used as extras in scenes filmed in Cedar City, and that a replica of the town of Cheyenne, Wyoming was built at the Iron Springs location, where approximately six miles of railroad tracks were laid for the production. According to an article in Life magazine on the making of the film, De Mille acquired more railroad cars than anyone outside the railroad industry had ever owned before. In order to legally operate its own private railroad, Paramount, according to publicity material, acquired a regulation railroad operating license, which was granted by the Interstate Commerce Commission. Technical advisor Lucius Beebe was a well-known columnist for NYHT.
       Time magazine reported that De Mille shot a total of 205,000 feet of film for the picture, which contemporary sources indicate was a $1,000,000 production. Farciot Edouart, Gordon Jennings and Loren L. Ryder were nominated for an Academy Award for their Special Effects work on the film.