10 deadliest U.S. tornadoes —
1.The "Tri-State Tornado," which killed 695 people and injured 2,027, was the deadliest tornado in U.S. history, according to the National Oceanic and Atmospheric Administration. The tornado traveled more than 300 miles through Missouri, Illinois and Indiana on March 18, 1925, and was rated an F5, the most powerful under old Fujita scale (winds of 260-plus mph).