The National Weather Service confirmed the tornado was on the ground and urged residents on Twitter to "seek shelter immediately if in the path of this dangerous storm."
An Illinois sheriff's dispatcher who declined to give her name due to department policy said there was widespread damage but no immediate reports of injuries when the tornado swept across the town of Hillcrest, about 80 miles west of Chicago.
VIDEO: Tornado touchdown in Rochelle, Ill.
TORNADO DAMAGE REPORTED IN ROCHELLE
Winnebago County Sheriff's spokesman Ken DeCoster said funnel clouds also were spotted near Rockford a few miles north but did not touch down. However, television footage showed multiple homes damaged in the unincorporated community of Fairdale.
The system, packing hail and damaging winds, was headed east as storms rumbled through the Midwest and Plains during the region's first widespread bout of severe weather.
PHOTOS: Hail, lightning, heavy fog in Chicago
The severe weather forced the cancellation of more than 700 flights at Chicago's O'Hare International Airport and flight delays of 90 minutes, and dozens of others were cancelled at the city's Midway International Airport.
Tornadoes were reported earlier Thursday near Peoria, and Dewitt, Iowa, but no damage was reported.
In central Indiana, a 75-year-old woman died Wednesday night after being swept into a rain-swollen creek near Indianapolis. Pittsboro Fire Chief Bill Zeunik said the woman, identified as Doris D. Martin, was clearing debris from a water-filled ditch in her front yard along with her husband when she fell in and was swept away into a drainage pipe. Martin's body was found in a creek nearly a mile away.
Minor injuries were reported Thursday in central Missouri when storms toppled trees, utility poles and billboards.
The National Weather Service's "enhanced risk" area stretched from northeast Texas to Michigan, Wisconsin and across the upper Midwest. Forecasters say Philadelphia, Washington and other parts of the Atlantic coast could see the same weather patterns Friday, including Augusta, Georgia, where the Masters golf tournament is taking place through the weekend.
"It's quite an expansive area," said Greg Carbin, a meteorologist with the National Weather Service's Storm Prediction Center in Norman, Oklahoma.
In Wisconsin, an interstate north of Milwaukee was closed for several hours Thursday morning after several vehicles became partially submerged in flood water due to heavy rain.
And in Michigan, lightning strikes caused a fire at a mobile home and a fire place explosion, according to authorities. No one was injured in either incident.
By mid-afternoon, temperatures in downtown St. Louis topped 80 degrees under bright sunshine. The balmy burst arrived in stark contrast to temperatures in parts of the northeast; freezing drizzle in New Hampshire delayed some school openings and more than 2 inches of snow postponed the first game of the season for the Portland Sea Dogs in Portland, Maine. null