Officials said six people in Illinois were killed when tornadoes and strong winds pummeled the central and southern portions of the state, prompting Gov. Patrick Quinn to declare seven counties state disaster areas.
The storm system also was blamed for two deaths in Michigan, reports said. One man died when his car was crushed by a fallen tree and a teenager was electrocuted when he touched a high voltage wire.
"We're all in this together," Quinn said during an on-the-ground assessment of damage in hard-hit Washington, a city of about 15,000. "And our state government is going to respond with every asset we have."
Quinn declared Champaign, Grundy, LaSalle, Massac, Tazewell, Washington and Woodford counties state disaster areas Monday.
"Our thoughts and prayers go out to everyone affected by yesterday's storms, including those who lost a loved one," White House spokesman Jay Carney said during the daily media briefing.
President Obama has been briefed and has stayed in touch with federal agencies, state and local partners leading the response in the affected states, Carney said.
"We urge citizens to continue to follow directions from their local officials," Carney said.
Before the storm system developed, the Federal Emergency Management Agency, through its regional offices, began to coordinate with state and local partners, Carney said.
The Chicago Tribune said there were 81 tornadoes sighted through the Midwest, 358 reports of damaging winds and 40 reports of large hail.
The most extensive damage was reported in Washington, Ill., hit by an EF4 tornado with winds of 170 mph to 190 mph. A 51-year-old man was confirmed dead and at least 70 people were treated for injuries at area hospitals, the Peoria Journal Star reported Monday.
"The devastation is just unbelievable," Washington Mayor Gary Manier said.
At least 400 homes were destroyed, the Journal Star reported. That number came from U.S. Rep. Aaron Schock, R-Ill., who surveyed the destruction early Monday.
The storm also caused heavy damage in nearby Pekin, East Peoria and Sunnyland.
Two fatalities were reported in New Minden after an EF4 tornado struck Washington County, the National Weather Service said. Three deaths were reported in Brookport just north of Paducah, Ky.
In Detroit, a 14-year-old boy was hospitalized after touching a low-hanging power line en route to school, The Detroit News reported.
The teen and his friends were on their way to school when he picked up the wire, apparently unaware it was live, Detroit Police Capt. Anthony Topp said.
As he was being shocked, the boy's hands were stuck gripping the wire, Topp said. His friends pried his hands loose using a piece of wood.
Emergency crews pronounced him dead at the scene, but medical personnel found a weak pulse when he arrived at a hospital, the News said.
The storm system moved to New England Monday, threatening morning commuters.
Fast-moving thunderstorms carried wind gusts of 40 mph to 55 mph to parts of the upper Northeast hours after they ripped across five Midwest states, through the Ohio Valley and across the Appalachians, bringing with them damaging winds, large hail and twisters.
More than 230 flights were canceled at Chicago's O'Hare International Airport because of the weather, and many other flights were delayed, The New York Times said. Flights were also delayed at Midway Airport.
In Indiana, tornadoes and storm damage were reported in 12 counties, Gov. Mike Pence's office said.
Officials in Kokomo declared a state of emergency and closed schools Monday, the city said on Twitter. All schools in surrounding Howard County would operate on a 2-hour delay.
In Missouri, a tornado may have hit Scott County, where heavy winds overturned three rail cars, blew over four mobile homes and damaged five homes, state emergency officials said.
More than 35,000 customers were without power, mostly in the St. Louis area, officials said.
High winds also knocked out power to at least 390,000 customers in Michigan and 75,000 customers in Ohio, utility companies and emergency officials said.
Storm gusts and threats of lightning in Chicago forced tens of thousands of fans at a Chicago Bears-Baltimore Ravens football game, eventually won by Chicago, to run for cover.
The game was suspended for 2 hours as fans took shelter in the concourse at Soldier Field.