A judge who moves from place to place within his area of jurisdiction, "riding the circuit."
In the early days of the United States of America, the country had a large land area and a relatively low population density. This became even more so when the Western Territories were acquired. Among other things, this meant that most towns and counties didn't need a full-time judge.
Instead, outside the major cities, a judge would be assigned a territory, the "circuit". He would move from place to place within the territory, "riding the circuit", trying any new cases that had come up since the last time he'd held court in that jurisdiction. Often, the judge would be accompanied by several "circuit lawyers" who traveled with the judge to find clients in need of their services (a town that doesn't need a full-time judge is unlikely to need full-time trial lawyers either). Abraham Lincoln was a circuit lawyer for a while.
Even the justices of the US Supreme Court initially had to ride a circuit to hear appeals when the full court wasn't in session. This is why people left the bench before dying, which unfortunately has apparently become par for the course.
As population density increased, cities and counties eventually needed full-time judges, but a remnant of the tradition remains in the names of some courts such as the Federal Circuit Courts of Appeals, the largest and most famous of which is the Court of Appeals for the Ninth Circuit (which covers the Western United States). It has also come to be used metaphorically: the Court of Appeals for the District of Columbia Circuit covers an area far too small to be a circuit in the traditional sense, and the Court of Appeals for the Federal Circuit doesn't have a region attached to it at all: its jurisdiction is limited by the subject matter of the cases.
In fiction, the Circuit Judge generally moves plots by his absence. If the protagonist is Wrongly Accused, he will have to cool his heels in jail until the judge comes, allowing the real crook to finish his evil scheme or leave town. Time for a jail break!
Another common plot is for a particularly despised accused criminal to be threatened by an angry mob while in jail awaiting the arrival of the judge. The Sheriff must either engage in Shaming the Mob until the judge can arrive, or undertake a dangerous cross-country journey with the alleged crook to where the judge is sitting so he can get a fair trial and be hanged legal-like. Occasionally the Sheriff will refer to the Marshal (meaning a Federal Marshalnote ) instead of the Circuit Judge as being the one to take the prisoners off his hands. This is connected, because the Marshal is the one who would escort the prisoner to the Judge.
In England and Wales, these were called "justices of assize", part of the Courts of Assize and finally abolished in 1972. The Courts Act that abolished the Assize Courts established the system of "Circuit Judges" in modern England and Wales (they wear purple robes and are often called "circus judges" for a laugh); although they might sit in a few different jurisdictions they don't follow a regular "circuit" as such. Circuit judges were also present in Medieval China, which, given that China is about the same size as the United States and often had (and still has!) relatively underpopulated "frontier" areas, should come as no surprise. They were particularly common during the Tang Dynasty.
The term has also translated into other professions; a Methodist minister responsible for more than one chapel or community is known as a "circuit minister" and his circle of "parishes" is the Circuit.
- Gold Key published four issues of a Judge Colt comic book about a gun-toting circuit judge.
- In Draw!, Starret manages to persuade the townsfolk of Bell City to wait until the circuit judge arrives so Holland can get a fair trail: confident that Holland will be acquitted once the facts are known. Unfortunately, the judge turns out to be a Hanging Judge who has a personal grudge against Holland.
- In Forty Guns, Judge Macy is the circuit judge for Cochise County, and completely in the pocket of Jessica Drummond. However, not even he will attempt to make a charge of murdering a U.S. Marshal go away.
- Luke Perry plays circuit judge John Goodnight in TV movie trilogy; Goodnight For Justice, Goodnight for Justice: The Measure of a Man and Goodnight for Justice: Queen of Hearts.
- Hang 'Em High is a version where the Circuit Judge is actually a major supporting character- and he is the original Hanging Judge (he was called that during his own lifetime) who is in charge of all cases in "Indian Territory" (Oklahoma). The main protagonist (Clint Eastwood) is the Marshal for the judge.
- The Sons of Katie Elder uses a combination of Wrongly Accused and Shaming the Mob, followed by moving the prisoners to where the circuit judge is.
- Judge Spicer is the circuit judge for that part of the Arizona Territory in Tombstone.
- In the Ben Snow story "Dagger Money", Ben is hired to protect a Circuit Judge.
- The Adjudicator in the Doctor Who New Adventures novel Lucifer Rising.
- Timothy Zahn's Dragonback series has a space version, where Judge-Paladins travel from planet to planet. In the fifth book, the main character is corralled into serving as a Judge-Paladin for an isolated group of aliens. He discovers shortly afterward that his parents were Judge-Paladins who were killed while visiting the same group of aliens.
- In the Heralds of Valdemar series, this is one of the main peacetime duties of the Heralds; one entire book, Arrow's Flight, consists of the protagonists riding circuit, and it makes up a majority of the plot of Bastion as well.
- There was a series of paperback westerns called The Judge by Hank Edwards about a gun-toting circuit judge.
- Judge Dee is the Tang dynasty-China version, moving from jurisdiction to jurisdiction every three years (so as to avoid getting judges too chummy with the locals, leading to corruption).
- SBS show The Circuit is about a modern day example of this, following the court as it goes on its circuit of remote Aboriginal communities in the West Australian outback.
- The Adjudicator in the Doctor Who story Colony In Space is a Circuit Judge IN SPACE! Or he would be, if he wasn't the Master.
- Frontier Circus: Ben is hauled before a circuit judge, who is a Hanging Judge, when he is accused of murder in "Quick Shuffle".
- In Here Come the Brides, William Zuckert appears in a few episodes as Judge Young or Judge Weems.
- Robert Vaughn played one of these in The Magnificent Seven TV series. He was a Reasonable Authority Figure and paid the Seven to keep the peace in the town during his frequent absences.
- The Outer Limits (1995) episode "Rule of Law" has a judge travel to an alien planet to preside over the case of an alien accused of attacking humans.
- Twin Peaks features a circuit judge who drives around in an RV hearing cases. In reality, Washington does in fact have a functioning legal system but Reality Is Out to Lunch in Twin Peaks.
- The Marukan regions don't have permanent settlements, just roaming clans of people Born in the Saddle, so their judges are similarly nomadic. Judges are usually partnered with a Cool Horse, like those bred locally, that helps them traverse the vast, roadless grassland.
- Imperial magistrates administer justice within a given region, which can be a city or a group of villages. One of the perks of being a magistrate is that they can "requisition" any food or shelter they want, and don't have to pay for it. Useful when you're exhausted from travelling all day...
- Many priests of the Immaculate Order are assigned to a backwater "territory" that they work in. Their duties include naming babies, blessing marriages, and exorcising ghosts with spiritual kung fu.
- Mage: The Awakening: The Silver Ladder Magical Society has Lictors, who circulate within a prescribed area to promote the core tenets of the organization and judge mages accused of crimes by their peers — mundane laws are beneath their notice.
- Warhammer Fantasy Roleplay: Travelling Judges are licensed by a magistrate to dispense justice on a specific stretch of land. Since they're usually failed city lawyers who have a financial interest in ordering as many trials as possible and rely on showmanship and fear to prop up their authority in the hinterlands, the quality of said justice is pretty patchy.
"No one except the gravedigger celebrates when a travelling judge arrives on the scene."