Back in jolly old England, King Henry II decided that folks who wished to have cases decided would not have to travel from remote places all the way to London to get a court date. He had his judiciary set up a traveling judge complete with recorders and lawyers who would go to different remote areas of the country on a set schedule, hence the name "circuit court".
The idea stuck when the United States was still mostly remote territory, especially in the wild west. The circuit courts would go from place to place on a set schedule to hear and try cases. Some Marshalls did the same thing. The villains in western movies had to have their henchmen break them out of jail before the circuit judge arrived to sentence the bad guy to hang by the neck until dead or until he spewed candy and cash like a piñata. The circuit courts would run until an area had too many cases, after which they set up a local judiciary.
Even though the judges don't run around in modern times except for Judge Dredd, the name stuck after all those years.
Iron Noder 2017