Autumn is a wonderful time of year in Yellowstone.
After Labor Day, things really close-up at Yellowstone Nat'l Park. For instance, there will no longer be any evening campfire programs after Labor Day. Usually,the stbles are closed around then. There are some campgrounds open, see other parts of the Total Yellowstone Page for information on campgrounds and lodging at that time of year. Check other pages in this site for trails open and general conditions at that time of year.