In 1927, it was reported that the storm crossed Illinois at the rate of 45 mph and that the width of the destructive path varied from a 1/4 to 1/2 mile. Today, it is estimated that this tornado had an average path width of 3/4 to 1 mile and that it was traveling at between 56 and 73 mph. It is estimated that the tornado stayed on the ground for about 219 miles, leaving ruin as it's aftermath.
So monstrous was this storm and so unprepared were the people in it's path, that the death toll reached almost 700 and that about 15,000 homes were destroyed.
In all, at least 695 died and 2027 were injured, mostly in southern Illinois. Three states, thirteen counties, and more than nineteen communities, four of which were essentially effaced (several of these and others never recovered), were in the path of the record 3.5 hour duration tornado. Total damage was estimated at $16.5 million; adjusted for wealth and inflation the toll is approximately $1.4 billion (1997 USD), surpassed in history only by two extremely destructive tornadoes in the City of St. Louis. These three events in terms of destruction, inferred by normalized monetary losses, are by far the most destructive (and expensive) tornadoes ever in the United States. Over 15,000 homes were destroyed by the Tri-State Tornado.
Nine schools across three states were destroyed in which 69 students were killed, more schools destroyed and more students killed (as well as the single school record of 33 deaths in De Soto, Illinois) than any other tornado in U.S. history.
The unusual appearance (due to its size) of the very fast moving tornado, best described by the witnesses along most of its path as an amorphous rolling fog or boiling clouds on the ground, fooled normally weather wise farm owners (and people in general) who did not sense the danger until the storm was upon them.
The tornado was accompanied by extreme downburst winds generally throughout the entirety of its course; the tornado and accompanying downbursts increased the width of damage from an average of 3/4-mile (1.2 km) (though at times over a mile [1.6 km] wide) to an area three miles (5 km) wide at times.
In addition to the dead and injured, thousands were left without shelter or food. Fires erupted, exacerbating the damage. Looting and theft, notably of the property of the dead, was reported. Recovery was generally slow with the event leaving a lasting blow to the region.