There are 3 routes that Jason will take in the camp. When you start up the game, he will take one of them. Cabin patterns can be identical, but Jason's starting point will not be. For every cabin pattern, there is an "A" or "B" path for Jason, and what I'd refer to as "A1."

This A1 is him starting right by the cave and moving left to attack the small cabin labeled as 3 in the A route image below. He'll still always alternate between routes A and B, but when you start the game he may start at A1 by the cave. This means cabin 4 can run left and immediately fight him as he makes his way to cabin 3, or cabin 2 can take the upwards path next to it and catch him as well. Not good for Any%, but worth pointing out.

Basically, Jason is going from house to house regardless of if anyone is currently hiding out in one. You can find him in a small cabin if he passes it, and oftentimes large cabins too. He continues along a specific path, and once it is complete, he heads back to the lake cabins to attack the children. So, what are his routes?

Represents where he will stop and attack someone (or enter that Cabin)

¤ Represents that Jason will enter this large cabin "Jason moves left here" is only mentioned because despite always appearing from the right side of the screen and running that way, he'll often actually be moving to the left.

If Jason has started on route A, he will follow route B after that. When he returns to the lake, he will switch back to A. Jason is constantly switching between route A and B. After route A, Jason exits the lake from the right side. He then moves left (appears to be down on the map) and he stops in the small cabin, before cutting through the woods to the southern part of camp. He then takes a very long path to the woods, cuts through it, and ends up north of the lake. He moves to the right and hits the lake cabins. After route B, Jason moves to the right and takes the path down, and then heads from northeast of camp into the cave area. He then exits the cave area and moves along south of the lake before taking the path up, moving left, passing the large cabin and entering the lake.

That may have been a little confusing, but see for yourself. Jason's patterns are extremely easy to follow. It is worth noting that if you start the game on route B, Jason will attack the southern cabin, completely ignoring the one he enters on the lake. Southern cabin and northeast cabin alarms go off instantaneously after start-up if there is a counselor in there.

Alternate images with his movement marked with lines can be found here