Lewis County, Missouri, was first organized as a separate county on January 2, 1833, from Marion County, Missouri. The county was named after Meriwether Lewis of the Lewis and Clark Expedition, who later became governor of the Missouri Territory.

The third and present courthouse dates from 1875. Lewis County is one of the few remaining courthouses in Missouri dating from the 1870s.

The towns within Lewis County are: Canton, Durham, Ewing, La Belle, La Grange, Lewistown, Maywood, Monticello (county seat), Steffenville, and Williamstown.