National Weather Service says a tornado that struck the central Illinois community of Washington had winds between 170 and 190 miles per hour.
The meteorologists say Monday that the storm had a preliminary rating of an EF-4.
The Tazewell County storm killed one person and injured dozens of others during Sunday's severe weather.
Meanwhile, a tornado that touched down in southern Illinois near New Minden, about 45 miles southeast of St. Louis, also had a preliminary rating of an EF-4. A northern Illinois tornado near Coal City had wind gusts between 111 and 135 miles per hour, making it an EF-2.
National Weather Service survey crews are heading out Monday to review damage near Peoria as well as Champaign and Vermilion counties.