Henry Fonda originally turned down the role of Lincoln, saying he didn't think he could play such a great man. He changed his mind after John Ford asked him to do a screen test in full makeup. After viewing himself as Lincoln in the test footage, Fonda liked what he saw, and accepted the part. He later told an interviewer, "I felt as if I were portraying Christ himself on film."
John Ford and producer Darryl F. Zanuck fought an extended battle over control of the film. Ford even had unused takes of the film destroyed so the studio could not insert them into the movie. One scene that Ford insisted on cutting was a scene where Lincoln met his future assassin, a very young John Wilkes Booth.
The brief "My politics are short and sweet" speech Lincoln makes when he announces his candidacy for the Illinois state legislature was taken from the speech Lincoln actually gave when he did that. When he says he's for "a system of internal improvements," he means what would now be called "investing in infrastructure," which in that era were principally roads and canals.
The trial of William "Duff" Armstrong, on which the fictionalized defense of Matt and Adam Clay shown in this movie is based, actually took place in 1858, when Lincoln was a successful railroad attorney and soon to be a nominee for the Senate. The other person accused of murder had been convicted in a separate trial several months earlier.
During the Springfield parade scene, the crowd chants "hayfoot, strawfoot!" at the militia soldiers as they march past. This is a reference to the army training practice of the time of putting hay on the left hand boot of recruits, and straw on the right hand boot, so that sergeants could get recruits to march in step. The largely rural farm boy population of the country that made up the army often didn't know left from right, but they knew the difference between hay and straw. The practice actually was most common in the Civil War.
Henry Fonda's makeup was based on photographs taken when Lincoln was about 45 years old and had lost weight due to the stresses of his job as a lawyer and his grief over the loss of Anne Rutledge; they were the earliest photos of Abraham Lincoln available at the time. It was not until years after this film was released that a photograph of Abraham Lincoln aged about 25 surfaced in a photograph collection. Ir was entitled "Photograph of a young man" and had been taken in 1844. The photograph shows that at the time it was taken, Lincoln was a sturdily built young man with a lean bony face and high cheekbones that made him very good looking if not handsome.
Originally John Ford did not want to direct Young Mr. Lincoln because there had already been two productions done about Abraham Lincoln as a young man.
"Academy Award Theater" broadcast a 30 minute radio adaptation of the movie on July 10, 1946 with Henry Fonda reprising his film role.
Included among the American Film Institute's 1998 list of the 400 movies nominated for the Top 100 Greatest American Movies.