Boil-water orders, arrangements to dispose of spoiled food, tree removal, power restoration and countermeasures to escape the hot, muggy weather ruled Independence Day eve, officials in the affected states said.
"If you need to charge your phone or you need Internet or anything, you show up here and it's literally a madhouse," Jacqueline Hirsch of Bethesda, Md., told WJLA, Washington, Monday of showing up at a library branch.
About 1.8 million people in 11 states stretching from Indiana to Delaware and Washington, D.C., were without power Monday night after strong storms accompanied by powerful winds swept across the states Friday.
Officials blamed Friday's derecho -- a widespread, long-lasting storm associated with a fast-moving band of severe thunderstorms in the form of a squall line -- for at least 18 deaths. Three other deaths were reported in North Carolina from a second round of storms Sunday.
For Tuesday, extreme heat warnings were issued for parts of Illinois, Indiana, Missouri, Kentucky, Ohio and Michigan, with the National Weather Service forecasting temperatures near or higher than 100 degrees F. Heat advisory warnings also were issued for parts of Nebraska, South Dakota, Wisconsin, Minnesota and Iowa.
After the storms swept the region, as many as 4 million customers were left in the dark Friday night and early Saturday, including about 410,000 in West Virginia, 400,000 in Ohio and 340,000 in Virginia.
Power and government authorities said some may not get electricity back until the end of this week.
The storm forced school cancellations and prompted orders to non-essential government employees to stay home.
West Virginia officials issued a statewide boil-water order. In Charleston, county park workers vowed to reopen Coonskin Park's pool by Wednesday so residents could try to get some relief, The Charleston Gazette reported.
"We're going to open the pool Wednesday," Kanawha County Parks Director Jeff Hutchinson said. "We have to, as hot as it is, and with people without power."
In Germantown, Md., crowds jammed one of the few public pools with electricity Monday.
"It's just great to get out of the heat. It's super hot without air conditioning in the house, so it's great to cool off in the water," Brian O'Keefe told WJLA.
In Baltimore, Mayor Stephanie Rawlings-Blake criticized Baltimore Gas and Electric Co. for moving more slowly in the city than elsewhere in the state, putting the elderly and the poor at risk, The Baltimore Sun reported.
"We might be annoyed, frustrated and hot as heck. We can get over that," Rawlings-Blake said. "If we lose a vulnerable citizen because of this heat, we can't get over that."
The 911 emergency telephone service in Fairfax County, Va., outside Washington operated at half capacity because Verizon's primary and backup power systems failed after Friday night's storm, leaving much of northern Virginia with no 911 service through the weekend.
Fairfax County is home of the CIA and four other top U.S. intelligence agencies.
AT&T, Sprint, T-Mobile and Verizon said they were trying to get generators to sites that lost power, The Washington Post reported.
Traffic lights remain out in many hard-hit locations, including Washington, and many secondary roads in affected states were closed, media reports indicated.
Virginia, Washington, D.C., Maryland, West Virginia and Ohio declared states of emergency because of storm damage.
Severe thunderstorms with strong winds and hail ripped through north-central Minnesota Monday, knocking out phone service in Bemidji.
Storms also struck parts of southern Illinois, Kentucky and Tennessee, the National Weather Service said.