The central Illinois community of Washington appears particularly hard-hit. A state official says emergency crews raced to the area amid reports that people were trapped in buildings.
But Patti Thompson of the Illinois Department of Emergency Management says communications are spotty and it's difficult to get information from the scene.
The National Weather Service says tornadoes touched down East Peoria, Washington, Metamora, Morton and other Illinois communities.
Officials couldn't say whether it was one tornado touching down or several.
Bad weather also caused officials at Soldier Field in Chicago to evacuate the stands and suspend the Bears game against the Baltimore Ravens.
Forecasters say it's all part of a dangerous weather system that has the potential to be destructive and deadly.
Russell Schneider, director of the weather service's Storm Prediction Center, says some 53 million people in 10 states are "at significant risk for thunderstorms and tornadoes."