Terry Moore claims that another actress was already hired for the role of Jill. She claims that she got the role by running to the end of the RKO lot and back after Ernest B. Schoedsack asked her, and claims that she was then hired on the spot.
A sequel called "Joe Meets Tarzan" was planned in 1950 and would have had Mighty Joe Young team up with Tarzan, played by Lex Barker, who had just filmed Tarzan and the Slave Girl. The film was canceled due to the disappointing box office of "Mighty Joe Young".
Even though the language spoken by the natives at the beginning is generally thought to be Swahili, screenwriter Ruth Rose just made it up. However, the censorship board still required her to produce a translation so they could be assured there was no offensive "language" in the film. She had had to do the same for the native speeches in King Kong sixteen years earlier.
In the 2011 version as seen on Turner Classic Movies, the "fire rescue" sequence, with a red background, is influenced by the 1980's "colorized" version. The "colorization" process, owned by Ted Turner and now "Time Warner", added color to previously existing all B&W films. Other "colorized" features in this genre included "King Kong", "The "Maltese Falcon" and even Shirley Temple film shorts. This trend continued through the 1990s although, as a whole, it is no longer popular with broadcasters and viewers.
Look for these unbilled stars of the future (and past): Ellen Corby (The Waltons) in the orphanage scene; William Schallert (The Patty Duke Show) as the gas station attendant; Kermit Maynard, singing cowboy, as Red in the roping scene; Jack Pennick, perennial John Ford extra, as the truck driver whose truck the heroes steal; and Irene Ryan (Granny in The Beverly Hillbillies) in the nightclub scene.
The "cowboys in Africa" sequence in this film used footage originally shot to be used in a planned but not completed follow-up to King Kong, "The Valley of Gwangi". That film (as The Valley of Gwangi) was eventually made by Ray Harryhausen.
The night club set was based on a real-life night club called the Cocoanut Grove, which was located at the famous Ambassador Hotel in Los Angeles, California.
The stock footage shot of New York's Times Square is actually from the mid-'20s. A marquee for Ernest B. Schoedsack's and Merian C. Cooper's "Grass, the Epic of a Lost Tribe", aka Grass: A Nation's Battle for Life can be seen in the lower right corner.
The strongmen who appeared in the "tug-of-war" scene with Joe were all professional wrestlers. They were: Sammy Stein, Slammin' Sammy Meneker, Max the Iron Man, Bomber Henry Kulky, Killer Karl Davis, Rasputin the Mad Russian, Wee Willie Davis, Man Mountain Dean, The Swedish Angel, and Primo Carnera. Carnera had briefly been the World Heavywight Boxing Champion. Dean, Kulky, and Davis also had careers in movies and TV.
This film was stop-motion animator Pete Peterson's first animating job. He was hired as a grip but became so enamored with stop-motion while watching Ray Harryhausen work that Willis H. O'Brien allowed him to try his hand at animating some scenes.
This was the first feature film to which Ray Harryhausen contributed stop-motion animation effects.
Though Willis H. O'Brien gets top special-effects billing, Ray Harryhausen actually did 85%-90% of the stop-motion animation for this film, although the animation is based on O'Brien's designs and storyboards.
When Joe smashes through the facade during the nightclub riot, the first scream you hear is that of Fay Wray, stock audio from the original King Kong, which was also produced by RKO.
When Mighty Joe Young gets frustrated, he pounds the ground with his fist. Ray Harryhausen was inspired to do this by the scene from King Kong where Kong pushes open the gates, then forcefully brings his hand down.
When Windy asks Gregg if he is from Texas, Gregg replies, "No, sir, Oklahoma; we rope and ride there, too." Ben Johnson grew up on a ranch near Foraker, Oklahoma, and had been a champion cowboy prior to coming to Hollywood as a horse wrangler.