Hi HE,
Williamstown is in Massachusetts, and is in fact your nearest large town to the trail's South "terminus". If you look at your Long Trail map, you should be able to see Williamstown just southwest of where the AT crosses the border into VT to become the LT. You can walk the Pine Cobble Trail in to start the LT, also evident in both map and guide.
I am a bit confused as to how/why you want to get TO the North terminus without driving, since as you say you are hiking South to North. Are you driving to North Jay to park, and then trying to get by bus to Williamstown, or are you making the entire trip (to and from home) without driving, and thus want to walk out at North Jay and find your way to civilization? So, I will address how you might get FROM the North terminus without driving.
Many use the services of
Rose Apple Acres for a shuttle from trailhead to Newport, VT, for example. You can also stay the night and/or leave your car there for $1/day. It used to be the case that you could pick up Vermont Transit in Newport, but I believe this is no longer so, as you have likely seen on the Vermount Transit website. I have, however, seen a recent reference to Rural Community Transport (RCT) - 802-748-8170 - as a means to get from Newport to connect with Vermont Transit, so you might give them a call.
I hope this helps . . .