Steve McQueen's vocals were dubbed by Billy Strange, a songwriter and musician who wrote songs for Elvis Presley and others and arranged and played guitar on records by Nancy Sinatra and the Beach Boys among others.
The denim shirt Steve McQueen wore in the movie was made by Wrangler (Model 27MW). This shirt is now a collector's item and highly sought after by denim enthusiasts.
Horton Foote was a native of Wharton, Texas, where portions of this movie were filmed. The Texas premiere of "Baby the Rain Must Fall" was held in Wharton on February 4, 1965, at the now-demolished Rio Theatre.
According to photographer William Claxton, the crew was shooting in Columbus, Texas on November 22, 1963 when the radio announced the assassination of President John F. Kennedy in Dallas. Everyone gathering around the radio was stunned, especially Steve McQueen who took it extremely hard and kept very quiet for the rest of the stay in Texas.