Director Damien Leone said that several big studios showed interest in financing this movie based on the unexpected success of Terrifier 2 (2022), even without a full script, but he turned them all down because he is certain that they would never let him film the opening scene alone, which he describes as "very controversial". Leone commented that the only reason that he can be so uncompromising in his depiction of horror and gore is because he finances his movies independently, creates all the special effects himself to keep costs down, and has no big studio breathing down his neck to make the movie more mainstream.
Legendary makeup artist John Caglione Jr most famous for working on The Dark Knight's Joker makeup told Damien Leone he was a fan of Terrifier 1 & 2 and offered to work on the film which Leone quickly accepted.
When making Terrifier 1 & 2 Damien Leone has stated in interviews that the crew consisted of only 5-10 people depending on the day with crew members working every position possible. For Terrifier 3 there were dozens of people on set every day with dedicated crew departments.
Distributor Cineverse had only one request and that was to make the film under two hours long. Damien Leone who served as his own editor again recalled ripping out pages while filming to make the film shorter realizing it would be too long and not have time to film the scenes. The ending was much longer and was cut down. Despite trying his best to meet this request Damien submitted his final edit at 2 hours and 5 minutes.
The rat tube scene truly made Art The Clown actor David Howard Thornton nauseous and he had to prevent himself from throwing up.