A derecho is a widespread, long-lived, straight line wind storm that travels over a great distance, usually hundreds of miles.
ComEd said 263,140 customers are still without power as of 9:30 p.m. Tuesday, and it could take multiple days to restore service. At one point, more than 800,000 customers lost power due to the storm, ComEd said. The south suburbs were hit hardest.
WATCH: ComEd gives update on Chicago area power outages
ComEd said towers and substations sustained damage in the storm, in addition to the widespread damage across northern Illinois.
"This is not just about wires and poles," said Rich Negrin, spokesperson for ComEd. "With a storm this bad with this much damage, it's not just a repair job. In some of the areas that are impacted, it's actually a rebuild. We're going to rebuild areas of the grid that have been significantly damaged by the storm. And that rebuild is not just a repair, it's going to take some time."
ComEd said the vast majority of outages will not be restored until Friday, and the areas that were hardest hit may not have power until 3 p.m. Saturday. Around 1,500 technicians are coming from around the country to help with the repairs, the company said.
In Harvey and Lombard, many elderly are sitting in the dark and the heat.
"He said, 'Go wake up our daughter' so I went up to grab her in the dark because there's no power, and that's when we heard the crash," said Jocelyn Enison, Lombard resident.
Jocelyn and her husband Steve are still recovering from the harrowing moments after a tree fell onto their home and crashed into their children's bedroom.
"It came through the kitchen wall, like straight in through and knocked our trash can over and shattered our guest room looks like a scene out of a movie," Steven Enison said.
Jocelyn was able to grab their daughter seconds before the crash.
"That was when I panicked you know and we just ran down as fast as we could and then things just continued to bang and crack," Jocelyn said.
The National Weather service confirmed a tornado touched down in Lombard, with winds up to 95 miles per hour.
In Harvey, multiple power lines were ripped from the ground, leaving a mess of wires for blocks.
"All this stuff came up; I've never seen nothing like this before in my life," said Annette Thurmond, who lives at the Turlington West Apartments, a high rise senior living facility.
Without electricity, residents there are left pleading for help.
"We don't have electricity so that means we don't have no means of fan, air, cooking or anything," Thurmond said.
"We need to be put up if this is going to last a long time because we in the second day already and we suffering," said Sheila Henderson, resident.
Residents said they can't wait days for the power to return.
"This is really scary for everyone that lives in this building because there's elderly people that's in here, a lot of them is on oxygen," Henderson explained.
"Somebody help us, we need some help now," said Rick Weaver, resident.
Residents said they've reached out, calling the Red Cross and city leaders but are still waiting unsure when their electricity will be back on.
ComEd said power likely won't be restored in Lombard until Saturday.
WATCH: Rogers Park residents survey tornado damage
The National Weather Service confirmed Tuesday that an EF-1 tornado touched down in the Rogers Park neighborhood on Chicago's North Side before moving over Lake Michigan and becoming a waterspout.
In Elmhurst, named in honor of its large collection of trees, branches and in some cases entire downed trees littered the streets. One apartment building had the roof partially torn off.
Fallen trees ripped down power lines, leaving residents in the dark. The entire downtown area of Elmhurst is also without power. Some larger merchants brought their own generators to keep going, but they are the exceptions. Even power to the traffic light at the main intersection in town is still off one day later.
ComEd crews are working on the situation, but in DuPage County alone there are tens of thousands without electricity.
"We've got outages in 58,000 homes," said DuPage County Commissioner Peter DiCianni. "ComEd's response has been weak."
WATCH: High winds down signs, trees, damage buildings
On Chicago's North Side, downed wires hit water and started a fire near Sheffield and Marcy, and in Lincoln Park a massive tree was uprooted.
Ray Velasquez came home to an uprooted mess, a tree that was there when he moved in 30 years ago ripped from the ground.
"I'm just fortunate that nobody was home. It would have been scary anyways, even if there was no bodily harm," he said.
WATCH: Storm downs massive tree in Lincoln Park
On Old Irving Park Road a crumpled, damaged sign slowed down traffic. A few miles away, around Cullom and Kedvale, the neighborhood was littered with huge trees and branches snapped like toothpicks.
"We had maybe 50 people come out of nowhere," said Ian Woodbury, who was helping to clean up. "First it was about 20 people and then it grew to about 50 to 60 people, coming around and sawing."
"I saw fences flying, everything, it was crazy," said Aziz Bayoueh, neighbor. "We started sawing trees down, this whole area was blocked. You could see trees split in half."
The ferocious winds blew apart a roof just north of Addison and Lake Shore Drive, and in Chinatown firefighters worked to make sure a roof didn't collapse completely.
In Roscoe Village trees snapped, roofs were damaged and fences were ripped from the round. People's Gas crews examined the storm damage in the 4700-block of North Paulina where a car was stuck under a downed tree.
In Plainfield and Joliet, police received multiple calls about power lines and trees down, as well as flooding, car crashes and road blockages.
Winds over 80 miles per hour have been recorded.
In River Grove, mature trees around 70 to 80 years old were shredded by the winds, leaving debris scattered all over the streets and blocking intersections.
"This is probably one of the worst I've seen in my 40 years here," said John Bjorvik, River Grove Public Works Supervisor.
Rozalie Andreychuk hid in her basement with her grandchildren.
"It was just like five to seven minutes of horrible wind," she said.
Her fear reminded her of the 1987 Armenian earthquake, when she survived hours in rubble.
"It was the same scared thing, but it is surprising; you do not have enough time to be scared," she said.
The fear also ran rampant through nearby Villa Park, where trees came down on cars and streets, and tore apart roofs. There were no reports of injuries there or in River Grove.
In Westchester, crews cleared debris from the streets; downed branches and parts of trees. At least one tree, judging by the char marks left behind, was likely struck by lightning, officials said.
"I was upstairs and I heard a big pop, just like that," said Carol Safelover, Westchester resident.
Safelover said she heard what sounded like a transformer blowing out when the wind and rain hit, but there was no damage to her home.
"Very thankful because we saw it blowing and it was like 'Oh my gosh!'" she said.
WATCH: Transformer explodes in Westchester
At Cermak and Boeger, a large tree fell in the front yard of Vicky Deanching's homes.
"We feel so lucky because it never touched my house," Deanching said.
In nearby Hillside, police said the winds may have blown out the windows at the Walgreens on 22nd.
The steeple of College Church in west suburban Wheaton was knocked over by powerful gusts.
"My wife Jen grew up going to this church and her parents go to this church and so it's such a landmark in the town so it's kind of devastating for the town to see this happening," said Jeff Otterby, Wheaton resident.
Pastor Josh Moody reassured his congregation this will be a unifier for church members.
"The Church is not the building the Church is about Christ, it's about the people and we have a great message of hope," he said.
No one was injured.
Called a derecho, the rare wind storm with power similar to an inland hurricane swept across the Midwest, blowing over trees, flipping vehicles, causing widespread property damage and leaving tens of thousands of homes without power.
The derecho lasted several hours as it tore across eastern Nebraska, Iowa and parts of Wisconsin and Illinois. A scientist at the National Weather Service's Storm Prediction Center says the storm had the wind speed of a major hurricane, and likely caused more widespread damage than a normal tornado. Officials in the Iowa cities of Des Moines, Cedar Rapids and Marshalltown say the damage is extensive.
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The Associated Press contributed to this report.