Trivia: In the scene where Alice finds Bill's body hanging on the back of the door to the generator room, the producers purposely did not tell Adrianne King what they were going to do to the body nor did they let her see the body beforehand. When she saw the body during filming it was for the first time. The scream she produced was genuine as it scared her badly. Needless to say, that entire scene was shot in one take.
Trivia: Betsy Palmer was never originally considered for the role. Shelly Winters was the first choice, but was not interested. Betsy Palmer ultimately took the role because she needed money for a new car, as hers broke down as she was traveling back home to Connecticut from New York.
Trivia: According to producer/director Sean Cunningham, Shelly Winters was the original choice for Mrs. Voorhees. He wanted a known actress whose career was winding down so the fee would be low. Winters wasn't interested. Estelle Parsons actually negotiated to be in the film, but ultimately backed out. Louise Lasser and Dorothy Malone were also considered before they finally would up with Betsy Palmer, who famously agreed to the role because she needed the money for a new car.
Trivia: The budget for this movie was $500,000.
Trivia: The music in this film and all other Jason movies where it sounds like "kkkkk" and fades is actually supposed to be Jason saying to his mother "kill, mom."
Trivia: Maybe not really trivia, but something interesting nonetheless. When the murders start happening at the camp, every time a death is shown the weapon used is something that was previously seen being used by one of the victims. Bill and Jack are killed by arrows, which were shown being used by Ned. Marcie is killed with an axe, which is something Steve was using earlier on a stump. Alice kills Mrs. Voorhees with a machete, which Bill used to cut some bush and kill a snake. We never saw the weapon used to kill Steve, while Ned and Brenda's deaths were off screen.
Trivia: It was reportedly makeup effects artist Tom Savini's idea to have Jason leap out of the lake at the end of the film for the final scare. He saw the movie "Carrie" shortly before filming and loved the final scare of that film, and suggested that this movie should end on a similar note with Jason attacking Alice.
Trivia: The film's original title was "A Long Night at Camp Blood." Director Sean Cunningham then suggested "Friday the 13th," because it sounded more dramatic. The script was then re-worked slightly to justify the title change. Reportedly, they had to pay off the producers of the 1979 film "The Orphan" to use the title, as it was released as "Friday the 13th: The Orphan" in some territories.
Trivia: When Betsy Palmer first read the script her reaction was "What a piece of shit!" But she figured it wouldn't matter because likely few people would see the movie anyway, much less remember it years later. Of course the movie was a big hit and spawned a decades-long franchise, and while she never said publicly whether she'd changed her mind about the film, she did genuinely appreciate everyone who did enjoy it and happily made public appearances to meet with the movie's fans.
Trivia: In order to attract investors, the producers bought an ad in the industry publication 'Variety' that simply displayed the title along with the text "The scariest movie ever made!" They were bluffing, of course, as they didn't have a script or even fully decided on the story concept at that point in time.