I forgot to mention
Fort Laramie National Historic Site in my previous post. A number of the original buildings have been restored/reconstructed and we found it to be a very interesting stop. I recall that there was a campground just as you turn off route 26 onto the road to the fort. Never stayed there though.
As a FYI, we have also used
Country View Campground in Ogalalla several times on the way west or east.
Please advise about the "interesting stops between Buffalo and Sheridan". Perhaps some things we can add to our list for the next trip.