Cooler air swept southward in the eastern half of the country, bringing down some temperatures by 15 or more degrees from Saturday's highs, which topped 100 in cities including Philadelphia, Washington, St. Louis, Indianapolis and Louisville, Ky.
For many areas, the cooler temperatures were ushered in by thunderstorms that knocked out power to thousands. In New Jersey, a line of strong, fast-moving storms knocked out power to nearly 70,000 on Saturday night.
The heat of the past several days has also been blamed for at least 35 deaths across the country. A 4-month-old girl died and a 16-month-old girl was hospitalized in suburban Indianapolis after both were found trapped in cars during 105-degree heat Saturday. Deaths have also been reported by authorities in Illinois, Maryland, Ohio, Pennsylvania, Tennessee and Wisconsin.
The heat caused highways to buckle in Illinois and Wisconsin, officials said. In Maryland, investigators said heat likely caused rails to kink and led a commuter train to partially derail Friday. No one was injured.
To stay cool, Americans tried familiar solutions - dipping into the pool, going to the movies and riding subways just to be in air conditioning.
Even the beach offered no respite. Atlantic City, N.J., home of the famed boardwalk, set a temperature record Saturday of 100 degrees.
Working outdoors in New Jersey on Saturday was Freddie Jackson, a 48-year-old Toms River man who sells roses by the dozen from his car, which was parked in a heavily shaded area off a major highway. Clad in shorts, sandals and a white T-shirt, Jackson said he would stay out as long as he felt safe - and business was good.
"I do this mainly to make a few extra bucks, so I'm not going to stay if I started feeling (the heat)," he said.
Jackson said his teenage daughter stopped by to bring him a cooler with several bottles of water, and he had a couple of ham and cheese sandwiches with him.
"I'm tempted to leave them out in the sun for a while and see if I end up with grilled cheese," he joked.
If Americans ventured outside to do anything, they did it early. But even then, the heat was stifling.
"It was baking on the 18th green," said golfer Zeb Rogerson, who teed off at 6 a.m. at an Alexandria, Va., golf course but was sweltering by the end of his round.
In South Bend, Ind., serious kayakers took to the East Race Waterway, a 1,900-foot-long manmade whitewater course near downtown.
"A lot of times I'll roll over just to cool off," said Robert Henry of Carmel, just north of Indianapolis. "The biggest challenge is walking coming back up carrying a kayak three-eighths of a mile in this heat."
In Manhattan, customers who stepped in to see "Jiro Dreams of Sushi" at an IFC movie theater were there for more than entertainment.
"Of course we came to cool off!" said John Villanova, a writer who was on his second sweaty T-shirt of the day and expecting to change again by evening.
He said that earlier, he rode a Manhattan subway back and forth for a half an hour, with no destination in mind "because it really keeps you cool."
In Chicago, street magician Jeremy Pitt-Payne said he has been working throughout the three-day stretch of triple-digit temperatures, but acknowledged that he might doff the Union Jack leather vest by the end of the day, even though it's part of his British magician character along with the black top hat.
His trick for beating the heat? He starts his shows at 2 p.m., "when the Trump Tower is gracious enough to block out the sun" along his stretch of sidewalk.
Zongker reported from Washington. Associated Press writers Verena Dobnik in New York, Ed Donahue in Alexandria, Va., Steve Szkotak in Richmond, Va., Mike Householder in Detroit, Carla K. Johnson in Chicago and Tom Coyne in South Bend, Ind., contributed to this report.