Alvin York himself was on the set for a few days during filming. When one of the crew members tactlessly asked him how many "Jerries" he had killed, York started sobbing so vehemently he threw up. The crew member was nearly fired, but the next day, York demanded that he keep his job.
Alvin C. York had been approached by producer Jesse Lasky several times, beginning in 1919, to allow a movie to be made of his life, but had refused, believing that "This uniform ain't for sale." Lasky convinced York that, with war threatening in Europe, it was his patriotic duty to allow the film to proceed. York finally agreed - but only on three conditions. First, York's share of the profits would be contributed to a Bible School York wanted constructed. Second, no cigarette smoking actress could be chosen to play his wife. Third, that only Gary Cooper, could recreate his life on screen. Cooper at first turned down the role, but when York himself contacted the star with a personal plea, Cooper agreed to do the picture.
Gary Cooper's acceptance speech typified so many of the actor's performances when he said "It was Sergeant Alvin York who won this award; Shucks, I've been in this business sixteen years and sometimes dreamed I might get one of these things. That's all I can say! Funny, when I was dreaming, I always made a good speech." As he left the stage, he forgot the Oscar on the podium.
When informed that Hollywood wanted to make a film about his exploits in World War I, Alvin C. York insisted that only Gary Cooper could play him. At almost 40 years of age Cooper was actually too old to play York - who was not quite 30 at the time of the battle - and York was informed of this, but he insisted that if Cooper couldn't play him, he would not allow the film to be made.
Gary Cooper, unable to participate in WWII due to his age and an old injury to his hip, felt strongly that this film was his way of contributing to the cause. Cooper later said, "Sergeant York and I had quite a few things in common, even before I played him in screen. We both were raised in the mountains - Tennessee for him, Montana for me - and learned to ride and shoot as a natural part of growing up. 'Sergeant York' won me an Academy Award, but that's not why it's my favorite film. I liked the role because of the background of the picture, and because I was portraying a good, sound American character."
Joan Leslie was 16 when she made this film, the same age as the real Gracie. Alvin C. York had made it clear that he didn't want any actress with any sort of notoriety connected with her portraying his wife. He specifically said, "No Ooomph Girls!", a clear reference to Warner Bros. contract player Ann Sheridan. Incredibly, Jane Russell was considered, but the wholesome Leslie was ultimately chosen.
The film turned out to be a highly accurate representation of history, mainly because of the studio's fear of lawsuits. Alvin C. York and several of the townsmen in Tennessee, including the pastor who counseled him, refused to sign releases unless the film was portrayed accurately.
When this film was being made, American public opinion was strongly isolationist and Warner Brothers initially worried that it would be condemned for being seen as too pro-war in attitude. Jesse Lasky went to great lengths to avoid marketing the film as a war picture. By the film's release, however, Adolf Hitler had conquered much of Europe and the public attitude towards war changed greatly, helping the film become one of the studio's biggest moneymakers of all time.
The scene where Alvin becomes converted because of the bolt of lightning was an invention of the screenwriters. In reality he was converted from his hard-drinking, roustabout ways to a Sunday-school teacher by his wife, and it was a longer and less dramatic process.
There were stories at the time of young men leaving the movie theaters after seeing the film and signing up immediately after. (War fever was particularly high in the USA at the time as the attack on Pearl Harbor had just happened.)
The actual firearm used by Alvin C. York to dispose of a line of seven Germans was not a Luger as depicted in the film, but rather a 1911 .45 ACP automatic. The Luger was preferred for the filmmaking, however, purely on the basis that they couldn't get the .45 to fire blanks.
The original film included a scene that featured the dance Alvin and Gracie were going to. It was cut in the theatrical release but the York family still has a copy of the movie with that deleted scene.
"The Screen Guild Theater" broadcast a 30 minute radio adaptation of the movie on January 18, 1942 with Gary Cooper, Walter Brennan and Joan Leslie reprising their film roles as Alvin C. York, Pastor Rosier Pile and Gracie Williams, respectively.