It all depends on the park that you're planning to visit. Those that have great foliage will have crowds around that time. Others at higher elevations may be closing down some services. You might want to see what the availability at campgrounds you're considering is for that time of year on recreation.gov.In your experience, do we need to make reservations in advance (and therefore, stick to a more rigid travel schedule)? Or, is there usually availability at nat'l park campgrounds in mid- to late-September/early October?