Deadliest United States tornadoes Deadliest United States tornadoes. The cyclone that swept Joplin, Mo., Sunday evening is the latest in a long line of destructive twisters. Here are the 10 most deadly U.S. tornado events on record, by the number of deaths. March 18, 1925 The Tri-State Tornado Number of deaths: 695 Where: Missouri, Illinois, Indiana Find estimated damage: The Tri-State Tornado is considered the deadliest tornado in U.S. history, totaling billions in damages. April 27, 2011 the 2011 Super Outbreak Number of deaths: 318 Where: Alabama, Georgia, Kentucky, Mississippi, Tennessee, Virginia Find estimated damage: Known as the 2011 Super Outbreak, these tornadoes spanned four days and caused widespread damages across several states. May 6, 1840, tornado Number of deaths: 317 Where: Louisiana, Mississippi Find estimated damage: Known as the Great Natchez Tornado, this storm moved along the Mississippi River and into Natchez, Miss., destroying buildings. Damages are unknown. Ma...