Marcus S. Wilcox served as a second lieutenant in Reid's Arkansas Battery, the "Fort Smith Artillery", at the Battle of Wilson's Creek. The battery was mustered out of State service on September 17, 1861, and all of its members were discharged. Many of them subsequently reenlisted in Confederate service in Provence's Arkansas Battery (1st Arkansas Light Artillery), but there is no record of further service in an Arkansas unit by Marcus Wilcox. Reid's Battery was organized in Sebastian County and vicinity.