I live in this area....my backyard !
The Adirondack park is huge (6 Million acres +). The two parks already listed (Lake George RV Park and Moosehillock RV Resort) are both outside the Parks true wild areas. They are Family focused, full hook- up campgrounds...both are first class operations and both are on route 149 and easy to get to via Interstate 87 (the Northway) or Route 4. Their are a number of parks in that area plus a New York State Park right on the shores of Lake George on Route 9. There are also a large number of campgrounds further up in the Northern sections of the Adirondack Park. The list is endless!
Getting from that area to or from Maine will require using route 4 from New York into Vermont and then connecting to interstate highways that will take you thru New Hampshire into Maine on the southern coast or via interstate 91 thru Vermont to connections to route 2 thru Vt., New Hampshire and into Maine. If my memory is correct route 2 (a 2 lane roadway) will bring you across Maine into the Bangor area with connections to Bar Harbor and Acadia on the coast of Maine.
Overall a great scenic trip!