85 years ago, on March 18th, 1925, the tornado formed about 1pm near Ellington, Reynolds Co., Missouri, and dissipated at 4:19pm, near Petersburgh, Gibson Co., Indiana.
The F5 tornado stayed on the ground for over 219 miles, it was about 1 mile wide and almost 1 mile high. There was no funnel, due to the tornado being so close to the ground. Winds probably exceeded 300mph. http://en.wikipedia.org/wiki/Tri-State_Tornado
My dad's family had just moved back to Mt. Vernon, Posey Co., Indiana, the year before, after living in the Missouri/Arkansas area for 24 years. Griffin is north of Mt. Vernon, by a few miles and Griffin was completely destroyed. 69 people died and 85 farms were devastated.
Three states were involved in the longest tornado in the history of the world: Southeastern Missouri, through Southern Illinois, and into Southwestern Indiana, which are all states that I am doing genealogy on. Estimated total number of deaths was 695, with 2027 injuries.
Another good link is the Princeton, Gibson Co., Indiana website: http://www.princeton-indiana.com/pages/history/tornados/1925_tornado-main.htm