If folks are looking for a less crowded Yellowstone experience consider visiting in the winter using snowmobiles. Of our 3 Yellowstone visits 2 have been in the winter on snowmobiles. We were skiing in Big Sky, Montana and did Yellowstone as a day trip. Our shuttle bus dropped us off in West Yellowstone for snowmobile gear and then we drove through the streets of W Yellowstone into the park entrance. The first time started out a bit cold at -20F and snowing but warmed up to 0F and the sun came out. The upper geyser basin was even more surrealistic with all the snow. Our 2nd trip on snowmobiles we headed up to Mammoth Hot Springs. Great wildlife viewing with bison and elk as they are hanging around the thermal features.
About 40X more visitors in the summer months than the winter:
stats