Stacey -
Much of northern Yellowstone actually borders the Gallatin National Forest. You can find out a ton of info on our Gallatin National Forest page:
http://www.parkcamper.com/Gallatin-National-Forest/gallatin-national-forest.htmI definitely recommend visiting this area if you want less people and to camp "in" the mountains. Just be aware that much of it is grizzly country and there have been incidents recently. Use good bear country methods (keep all food, wrappers, scents out of your tent and sleeping clothing).