Depending on where you are, I'm sure there is a club near you.
In addition to the ones already mentioned - there are many chapters of the Green mountain Club (
www.greenmountainclub.org) in VT and the Adirondack Mountain Club (
www.adk.org) in NY. There's also the NJ Trails conference (don't have the URL)
Others exist for the Catskills region, Bigelows region in Maine. (sorry, I don't know much south of there... but I'm sure there are many.)
Also look into local universities/colleges - Dartmouth Outing Club might be able to point you in the right direction.
I'm with a club with our local YMCA - in Montreal.
We also have many "for profit" outing groups in our region....
Just ask around, I'm sure you'll find more clubs than you can shake your walking stick at!