Just north of the town of Granville, in middle Vermont, on Route 100. The falls are literally on the side of the road, with the parking area a few hundred feet north of the falls.
Driving along Route 100 north in middle Vermont can be a very pleasant experience. The towns are small and quaint and the scenery can be very dramatic, especially during peak foliage season of early October. However, you will also experience large crowds and expensive lodging (if available) during this time. I prefer winter in Vermont when nature photographers have the woods pretty much to themselves. Moss Glen Falls is easy to miss. It's literally on the edge of the road and you may only glimpse it in the corner of your eye if you're concentrating on the traffic; however, it is clearly worth a u-turn. A wooden boardwalk brings you to a limited vista point where photography is ok, but I prefered to walk down off the road's edge (careful of the slippery rocks) and set up a tripod where the stream and waterfall are both visible. An exposure of several seconds with an f stop of F 16 or so will keep everything sharp and impart a cottony look to the flowing water. Nikon F100/17-35 f 2.8 zoom at 17mm/ Fuji Velvia 50.