13 Things You Didn't Know About Friday The 13th
9. Mrs Voorhees And The Odd Coincidence Part 1
In the film, Betsy Palmer plays Mrs Voorhees, who’d been the cook for Camp Crystal Lake's in 1957. According to the backstory that Palmer wrote for Voorhees to help her get into character, she'd taken the job to allow her handicapped son the chance to be around other kids, but the camp counsellors had been more interested in screwing around than looking after the kids, and Jason, a poor swimmer, had drowned.
The following year, Voorhees murdered the two counsellors whose negligence had allowed her son to die. The movie implies that ever since then, Mrs Voorhees had been obsessed with Crystal Lake, setting fires and poisoning the water in an effort to keep the camp closed and only coming out to resume the murders once her efforts at sabotage began to fail.
In real life, this was all kismet: along with her father and her brother, Palmer herself had actually spent summers in a place called Crystal Lake as a child, although that was near Warsaw, Indiana, not New Jersey.