Although Jay Ose is credited only with playing the small part of "2nd Fertilizer Man," the Los Angeles Times reported during filming that he was on set to coach George C. Scott in his role as a con artist. Ose, a professional magician and card dealer, is apparently the man whose hands appear in the close-up shots of Mordecai Jones doing particularly elaborate card tricks.
This movie was filmed in Lexington, Kentucky and surrounding small towns, including Richmond, Winchester, and Irvine, Kentucky. The scene which shows the green bridge and A&P store was shot in Irvine, a small Appalachian town in Estill County, Kentucky. Townspeople had never witnessed a movie being made, and many stood excitedly watching the process. Highly acclaimed actor Harry Dean Stanton was born in West Irvine, which is very close in location to shots taken for this movie. However, Stanton had long since departed for Hollywood, and had already starred in many classic hit shows and movies by that time.
Due to a prolonged period of inclement weather, Lawrence Turman rented Lexington's G. T. Vaughn tobacco warehouse, which would provide 200,000 square feet of makeshift studio space for nine interior sets.
When a secretary working on the film was killed in a car accident, actor Jack Albertson took up a collection to pay for the funeral. According to George C. Scott's longtime friend Del Acevedo, Scott told Albertson: "[S]end me the bill for the funeral and whatever you collect, give to the family to help them along."
O Magnífico Farsante (1967) was Canadian actor's Michael Sarrazin's first leading role in a major film, though he had appeared in a couple of low-budget films and a TV shows before this film. In this film, he received an 'introducing' credit. He played the character "Curley Treadaway."