Character mistake: When Festus is arresting his cousin portrayed by Shug Wooley, as he helps him up off the floor, he distinctly calls him Henry when that cousin's name is Emory.
Suggested correction: He calls him "Emery." He even says his name earlier in the scene shortly after he walks in and he pronounces it the same way. There wasn't even a character or actor in the episode named Henry, so it's not as if he mixed up the name.
Factual error: In the opening dialogue by Matt Dillon on Boot Hill, the last shot of a tombstone has the date of 1982.
Suggested correction: It's not a "9" but an "8." The two 8's don't really match, but you can see the other tombstone with a similar "8." It's 1882.