The Monticello area, like much of Lewis County, was pro-Confederate during the American Civil War. Perhaps the town's most significant contribution to the Southern cause was one of its most notable citizens, Martin E. Green. He and his brother, U.S. Senator James S. Green had come to Lewis County from Virginia in the mid-1830s. While James became a lawyer and politician, Martin operated a successful sawmill near Monticello. He would also enter politics, becoming a judge of the Lewis County court. With the outbreak of the Civil War and a riot at Canton on July 4, 1861, Judge Green called on Lewis County's pro-Confederate citizens to assemble under the banner of the Missouri State Guard at a training camp on the Fabius River at "Horseshoe Bend" not far from Monticello. A few weeks later Green's forces would be defeated by pro-Union Missouri Home Guards at the Battle of Athens in neighboring Clark county. Green and his band of northeast Missouri cavalrymen would go on to fight at Lexington, Missouri, Battle of Pea Ridge (Arkansas), and elsewhere in the trans-Mississippi theater. Green would rise to the rank of Confederate Brigadier General before being killed at the Siege of Vicksburg in late June, 1863. Meanwhile, other units of Confederate bushwhackers and pro-Union forces would continue to clash in the county. On July 9, 1862 Confederate guerrilla leader Raphael Smith, a pre-war tanner in the area, raided Monticello with a force of eighty men. There they captured or "liberated" various supplies and forced one the towns ardent Union supporters to take an oath of allegiance to the Confederacy. Smith's group would again attempt to raid Monticello a few weeks later on September 1, but were driven off by the approach of a 300-man Union cavalry patrol.