General Tri-State Tornado Facts. Findings from modern weather records and research suggest that a tornado that endures as long as the Tri-State Tornado actually results from a cyclical supercell rather than one massive storm. The Tri-State Tornado occurred on Wednesday, March 18th in 1925. 1. Three states were affected by the Tri-State Tornado: Illinois, Indiana and Missouri. It is the deadliest tornado in U.S. history with 695 confirmed fatalities. In this theory, the storm continuously evolves, and the decay of one supercell leads to the development of another—and so forth. Tri-State Tornado of 1925, also called Great Tri-State Tornado, tornado, the deadliest in U.S. history, that traveled from southeastern Missouri through southern Illinois and into southwestern Indiana on March 18, 1925. 11 Tri-State Tornado Records. 1925's Tri-State tornado is considered the deadliest in United States history. The Tri-State Tornado is considered the most intense tornado in recorded history. It is the second deadliest tornado in world history, only surpassed by the 1989 Daultipur-Saturia Tornado. Known as the “Tri-State Tornado,” the deadly twister began its northeast track in Ellington, Missouri, but southern Illinois was the hardest hit. The storm completely destroyed a number of towns and caused 695 deaths. The Tri-State Tornado is currently the U.S. record holder for longest tornado track (219 miles), most deaths in a single tornado (695), and most injuries in a single tornado (2027). While it occurred before the modern record, it is considered by all accounts to be a F5/EF5 Tornado. The damage was estimated at $16.5M and in 2011 adjusted dollars that is approximately $1.4B. Passing through eastern Missouri, southern Illinois and southern Indiana, it killed 695 people and injured an estimated 13,000 people, causing $17 million in property damage. Beginning in Ellington, Missouri and ending in southern Indiana, southern Illinois was the hardest of the three states hit. The Tri-State Tornado of 1925 has been labeled the worst tornado in U.S history.