Visible crew/equipment: When Chester and Cassie are in The Cabin, Chester is looking through the picnic basket while Callie holds on the Indian's hand and talks to him. In the scene behind Callie is an unidentified man who disappears when the scene cuts to Chester. (00:47:00)
Continuity mistake: When Matt and Chester get up in the morning, Chester is in a chair with a blanket covering him up to his chin. Camera shot changes to Matt's point of view and Chester has no blanket as he speaks. Camera shot changes back to the prior viewpoint and the blanket has reappeared. (00:21:40)
Continuity mistake: Marshall Dillon buries an outlaw at Sarah's place. He installs a wood cross at the grave. Sarah comes out and they talk. When she leaves, the scene cuts back to Dillon and the cross is missing.
Continuity mistake: Matt arrests two cattle rustlers and ties them up back to back in their wagon for the ride back to Dodge. The two rustlers later change positions in the wagon for no apparent reason. (00:26:00 - 00:29:00)
A Quiet Day in Dodge - S18-E19
Other mistake: Festus returns from catfish fishing carrying a gunny sack full of fish that is bone dry when it should be dripping wet or at the minimum damp from the fish.
Factual error: In the opening scene Marshal Dillon walks in Boot Hill cemetery. Dates on grave markers include 1883 and 1882. At the end of the episode Marshal Dillon and Chester discuss an Army deserter who had just been acquitted of a murder that Marshal Dillon was sure he had committed. The army deserter is being sent back to his unit to fight the Sioux and Cheyenne Indians under Gen. Custer. The viewer knows the army deserter will soon die in the Battle of Little Big Horn on June 25, 1876 - seven years before the date on one of the grave markers. (00:00:25 - 00:24:30)
The Fires of Ignorance - S20-E17
Continuity mistake: When the school teacher is questioning the father in court, he places a farmers' almanac on the judge's bench and walks away leaving it. When camera cuts to the judge with a clear shot of where the almanac was left, it is not there. (00:44:00)
Other mistake: A female rancher hires workers to dig a water ditch on her property and hires two gunmen for protection. The other ranchers, upset about losing their water supply, vote on whether to fight the woman or let her be. Each man votes by dropping a small stone into a barrel. A black stone means "fight" and a white stone means "let her be." When the barrel is emptied, there are 23 black stones. However, there are only 14 ranchers in the room.
Factual error: There's a 1930s/40s vintage car in the background of this episode. The scene is associated with the marriage. Chester and Matt hear a gunshot and the scene then pans to some buggies, horses and people at The Wedding area. Matt and Chester jump on horses and ride out, and if you look closely at the background, there's the car, traveling by for about two seconds.
Factual error: The George Washington $20 dollar gold certificate bills shown when the wife finds the stolen money were issued in 1906. (00:26:00)
Other mistake: The pot belly stove in the Sheriff's office has the stovepipe exiting through the front wall, there is no stovepipe or chimney showing on the front of the building?
Visible crew/equipment: When Festus has put a false article regarding a gold strike and the people are rushing out of town, there is a shot in which the view is head on to the street full of riders and wagons as people are leaving town and the roof of the set is visible over the street instead of sky.
Character mistake: Reward poster on the pillar for Matt says "Matt Dillion", not Dillon.
Other mistake: Jeb throws a big party at Miss Kitty's saloon and pays for it with a poke full of gold. Sam the bartender weighs the gold and says it is worth $420. Kitty later gives the poke of gold back to Jeb and tells him, "The party is on me." Sholo, Jeb's mining partner, says, "There's $700 worth of gold there. "
Nitro! (2) - S12-E29
Revealing mistake: 15 minutes in, they blow open a safe. The door starts to open before the explosion goes off.

Catawomper - S7-E19
Visible crew/equipment: When Marshal Dillon helps Kate down off the carriage, the moving boom mic casts a shadow on the wall on the left side of the screen. (00:23:05)
Visible crew/equipment: During the sequence with the fire going on in the town, there is a shot with several guys on horseback riding parallel with the camera. They're talking while riding. Look at the lead horse. The shadow of the boom mic is extremely obvious. (00:15:45)
Other mistake: Near the end of the episode, there's a gunfight, and they show Matt Dillon reloading his gun. Just after the gunfight, you can see the extra bullets on his gun belt. None of the bullets are missing.
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.