The deadliest tornado in Illinois and U.S. history, was the Great Tri-State Tornado on March 18, 1925. It ripped through not only Illinois, but also Missouri and Indiana. The monster tornado had a 219-mile path, averaging 3/4 miles wide, reaching a record mile wide in some areas.
It’s devastating F5 winds wrecked havoc for a relentless 3.5 hrs starting at 1:01 p.m. local time close to Ellington, Missouri. It finally dissipated at 4:30 p.m. just southwest of Petersburg, Indiana. A total of 695 people were killed and over 2,000 injured, according to the National Weather Service. About 15,000 homes were destroyed.
The worst tornado ever to hit Chicago was on April 21, 1967. The area was hit by at a family of 10 tornadoes, three of which were typed the violent F4. The twisters left 58 dead and more than 1,000 injured. Damage was in the range of half a billion dollars (2006 dollars).
The most violent of the F4S formed in Palos Hills in Cook County and traveled through Oak Lawn and the south side of Chicago. In that one alone, 33 were killed and about 500 injured. The twister was 200 yards wide and carved a swath of damage ranging 16 miles.
Only one F5 tornado has ever hit the Chicago area. It was on August 28, 1990. This tornado formed near Oswego and passed through Plainfield, Crest Hill, and Joliet on a 16-mile path of destruction. It left 29 dead and 350 injured. Damages were estimated at $165 million.
The F scale, or Fujita scale, goes up to F5. F4 signifies winds of 207-260 mph, while an F5 is 261-318 mph.
Central and Southeast Illinois have seen more tornadoes over the years, more than other parts of the state. This National Weather Service map shows the number of tornadoes reported across the Lincoln NWS’s County Warning Area between 1950 and 2012. McLean County has seen the most tornadoes with 103 in 62 years.