Other mistake: On the back cover of the DVD it says "An idyllic summer turns into a nightmare of unspeakable terror for yet another group of naive counselors." The cast of this film are Chris's friends, not camp counselors.
Continuity mistake: After Edna yells through the window at Harold for knocking down the clothesline pole, she slams the window shut and the end of the curtain gets trapped under the window. Then the scene cuts to show Edna from the inside, and look at the curtains from this shot. They are now hanging straight down, just like it should be and aren't trapped. (00:08:10)
Continuity mistake: When they arrive at the lake and get out of the van, the long shot from the passengers' side shows Chris getting out and slamming her door, but then the next shot from the driver's side shows her getting out and slamming the door again. (00:21:55)
Continuity mistake: When Jason swings the machete to kill Andy, he swings vertically, which would have cut him between the legs down to his head, as he was walking on his hands. Later when Andy is shown, he is cut horizontally at the waist. (01:00:15)
Deliberate mistake: After Chris gets stuck on the bridge and is trying to restart the van, a shot out the back window shows Jason running towards the van. He is badly limping and holding his knee because Chris just stabbed him in the knee. In the next scene, when Jason is chasing Chris away from the van, and for the remainder of the movie, Jason no longer limps. He walks and runs normally.
Plot hole: Jason is standing in plain sight of Chris and her friends and no one even notices? The sun is even shining on him. (00:35:55)
Plot hole: When Loco goes up the ladder in the barn, he looks around for Fox. But he doesn't see her hanging by her neck until he turns around to go back down the ladder. There's no possible way he didn't see her the first time he went through there - there's nothing blocking the view.
Revealing mistake: Near the end of the movie, as they are about to walk out of the barn thinking everything is over and Jason has been hung on the hook from the loft, if you look between the cracks of the barn door, you can see Jason being lowered right before the doors open.