Wilmington Notch Falls is a thin, but powerful 50-foot cascade in the West Branch of the Ausable River.
The best view of the falls is from the Wilmington Notch Campground off NY 86.
According to those who have visited the falls, if you tell campground officials you're there to see the waterfall, they will let you in for free as long as you're out within 30 minutes. Otherwise, there's a day-use or overnight fee.
Note that you will need to climb down (and back up) an embankment in order to see the falls, so be prepared for a short but strenuous climb.