Northeast Association of 4WD Clubs
The NEA and its member clubs have access to some really nice private properties.
You did not say much about the type of wheeling you do. Easy, moderate, extreme, do you trailer your rig, etc? The answer will determine which clubs would be best for you.
New England Jeepz (link in sig) has quite a few members in the greater Boston area and access to their own private properties in addition to NEA properties. NEJz leans towards the upper end of the difficulty scale but we do have runs suitable for lesser built rigs.