The
circuit rider was best known in eighteenth century
America when
settlements were few and far between and could not always provide enough of a
congregation to support a
preacher for each town. So a
minister would ride on
horseback from place to place, holding services in each location in whatever building would hold the congregation,
christening whoever had been born since the last visit, saying
funerals over the newest graves, and also carrying
news from town to town. It might take five weeks to make the entire round. The
Methodist church seems to be most well known for sending out these "
backwoods preachers";
John Wesley first used the system in England when forming the denomination, and
Francis Asbury followed his lead in the New World. However,
Lutheran churches in Upper
Michigan are still using the term for their traveling lay ministers.
The phrase was also used to describe judges, both state and federal, who rode around hearing cases in different locations throughout the thinly settled states. The first U.S. judges rode circuits in 1790, and such people as Abraham Lincoln rode along with the judges as lawyers to offer their services in the cases being tried.
A Google search reveals that the phrase is now being used for just about anyone who travels from place to place for work, be it teaching, troubleshooting machines, working in local government for multiple towns, or whatever. There seem to be several newsletters using the name as well.
Sources: http://www.crrange.com/page44.html
http://www.encyclopedia.com/printablenew/02771.html
http://users.michiana.org/unita/sermons/2001-0610.html
http://www.thelutheran.org/9608/page12.html
Odie B. Faulk, "Circuit rider," Discovery Channel School, original content provided by World Book Online, http://www.discoveryschool.com/homeworkhelp/
worldbook/atozhistory/c/115860.html