I can't remember the specific spot the first time I did the trail - there was a good campsite along the river maybe about 3/4 of the way to the falls along the Jack's River Trail.
The second time (when I lost my food), there is a good campsite a few minutes walk from the falls on the other side of the river from the trail. Were were able to hop across on rocks to the other side and it was a nice campsite right along the river with room for several tents.
If I remember correctly, there aren't any camping restrictions along the trail and there are several good areas to camp. Sorry I can't be more specific on the campsite locations.