Edna May Wonacott, who plays young Ann Newton, and Estelle Jewell, who plays Charlie's friend, Catherine, were both locals of Santa Rosa, where the film was shot on location. Many of the film's extras were also locals of the town, which was too far away from Hollywood to be affected by Actors Guild guidelines demanding the use of professional actors.
"Shadow of a Doubt" was the script title but was listed as only a "temporary title" until a better title could be found.
The name of the waltz that is referred to throughout the film is "The Merry Widow Waltz".
The portrait that hangs on the wall of Charlie's room to the right of her door is one drawn by Willy Pogany of actress Mary Philbin, who was a leading lady at Universal just 20 years before.
The name "Charlie" is spoken approximately 170 times.
Hitchcock wanted William Powell to play Uncle Charlie, but MGM refused to lend the actor for the film. So the role went to Joseph Cotten.
In 1959 interview, Teresa Wright said that this was her favorite film.
Uncle Charlie arrived in Santa Rosa on August 22 or 23, 1942: the headlines in the paper were "Brazil Declares War", which had happened on August 22. However, there are also two clues that point to the film being set in pre-Pearl Harbor America (prior to Dec. 7, 1941, when the Japanese attacked the United States in the Pacific, bringing the U.S. into World War II). In the first dinner scene after Uncle Charlie's arrival, he presents gifts to the Newton family, including a pair of photos of their parents to Mrs. Newton, his sister. She remarks that the photos were made in 1888, and her son exclaims "Fifty-three years ago!" That would make the year 1941, not 1942. Also, when Uncle Charlie and his niece visit her father's bank, there's a sign on a teller's cage urging customers to "Buy Defense Bonds!" U.S. government bonds were renamed "War Bonds" after Dec. 7, 1941; "Defense Bonds" were sold prior to that date. The "Brazil Declares War" headline probably reflects a news story contemporary with the shooting of the movie, but it's in the wrong time frame for the action of the story itself.
The bridge in the opening of the movie is the Pulaski Skyway that carries U.S. Routes 1 and 9 between Jersey City N.J. and Newark N.J.
The area shown after the Pulaski Skyway is known as the Ironbound section of Newark, NJ, which has also been used for location shots in Wise Guys (1986) and _War of The Worlds (2005)_.
In his interview with François Truffaut on "Shadow" (first published in 1967), Alfred Hitchcock said the dense, black smoke belching from the train that brings Charles Oakley to Santa Rosa was a deliberate symbol of imminent evil.