is a county in the southern portion of the U.S. state of Missouri. As of the 2010 census, the population was 8,441. Its county seat is Eminence. The county was officially organized on January 29, 1841, and was named in honor of George F. "Peg-Leg" Shannon, a member of the Lewis and Clark Expedition. It is the second-largest county by area in Missouri.
The Great Tri-State Tornado of March 18, 1925 appears to have begun in Moore Township; most likely as constituent tornadoes of a tornado family preceding the infamous very long tack tornado that went on to kill 695 people across southeastern Missouri, southern Illinois, and southwestern Indiana over the next several hours.