The 1990 Plainfield tornado was a devastating tornado that occurred on the afternoon of Tuesday, August 28, 1990. The violent tornado killed 29 people and injured 350. It is the only F5 tornado ever recorded in August and the only F5 tornado to ever strike the Chicago area.
It formed from a supercell thunderstorm which initially formed in the vicinity of Janesville in south central Wisconsin and produced a tornado near Pecatonica in Winnebago County, Illinois which touched down at 1:42 p.m. That tornado did not live long, but the storm continued to move southeast towards the Aurora area, but with no official touchdown and only minor roof damage. Continuing southeast, a tornado touched down and rapidly strengthened into a violent F5 tornado.