Fall visit to the Black Hills

We were in the Black Hills last year from August through late October. September is still fairly busy, but you should be able to move around most areas without a reservation. The exception, I think, would be Custer. In addition to the buffalo roundup, there are quite a few biking events on the Mickelson Trail, which runs right through Custer. We used Custer as a base and drove the car to the sites we wanted to see, and to view wildlife in the evening in Custer State Park. By the first part of October, things are starting to close for the season. We have visited the Black Hills many times, and always find something new and different. Have a great trip.

If you should be staying around CSP Buffalo Round Up time, you should make a resevation to secure a prime site, not a left over.

X2

We enjoyed the lack of crowds and cooler temps Oct 2015. Parks had plenty of room.

you should be okay re no reservations, but toward the last week of Sept, Custer State Park has an annual Buffalo Roundup festival that draws over ten thousand people, so you might have trouble finding a site down around Custer.
It's pretty in the Black Hills in mid to late Sept.

It should work in Sept. after school has started. We do that sometimes and will make a reservation one or two days in advance if we think it necessary. Weekends could still be busy then.
Milt