Some 200 cities in the West hit daily record highs last week, including Las Vegas at 117, and Death Valley soared to 129, the weather service said.
The blistering heat has caused numerous deaths this summer. In the Phoenix area alone, 24 people, most of them homeless, have died.
Police there were hitting the streets in many cities, reports CBS News Correspondent Kelly Cobiella, handing out water, and checking for the hum of a running air conditioner.
At least four deaths have been blamed on the heat in Missouri, including a woman found dead Sunday in a home without air conditioning. Four people have died of the heat in Oklahoma, two of them young children left in cars, and at least three heat deaths have been tallied in New Jersey.
As a large swath of the U.S. suffered through another miserably hot day, people cranked up their air conditioners, headed to swimming pools and ran through sprinklers to try to stay cool.
"It's like stepping into a sauna. The humidity is a new thing," said Barbara King, 26, of Aberdeen, Scotland, who was vacationing in Chattanooga, Tenn.
In North Carolina, Kent Struble said residents in the Raleigh area have been calling his ice business to order 15-pound blocks to drop into their swimming pools.
"Like I tell them, if you've got 50,000 gallons of water and you're trying to cool down, you know what you're up against there," he said.
Demand for electricity to run air conditioners hit record peaks Monday throughout Ohio and the Tennessee Valley. The load on generators caused a power outage in St. Louis County, Mo.
A break in the heat was on the way, at least for the Midwest.
A cold front brought rain Monday to parts of Iowa, Minnesota and Wisconsin, and was expected to cross Illinois, Missouri and Indiana on Tuesday, said Ed Shimmon, a weather service meteorologist in Lincoln, Ill. Eastern states should feel relief by Wednesday.
When they could, many people avoided being outside. At the Indian Valley Golf Course in the Cincinnati suburb of Newton, 20 people had been scheduled to play in the morning and only three showed up, said Dave Weber, who works in the pro shop.
Greg McCullom, of Cincinnati, decided to skip a doctor's appointment to avoid aggravating his asthma.
"I just got off a bus, and I'm going to catch the same bus home," said McCullom, 52, as he stood in the shade near a downtown bus stop. "As soon as I got off the bus, I had trouble catching my breath. I didn't know it was this bad."
In downtown Columbus, Tom McCullough, 55, walked by a row of sweltering people at a bus stop, handing each a dripping cold bottle of water.
"They looked hot," he said, adding that he bought a case of water on his way to work and chilled it in his office refrigerator.
Despite the giant fan and ice packs, Madalyn Lynch's boxer was still panting, drooling and not obeying commands in the exhibition ring at a 4-H dog show in northern Ohio.
"When he's supposed to sit, he just lays down," said Lynch, 18, who braved the scorching temperatures with her dog, Courtley, to attend the Seneca County Fair in Tiffin on Monday. "It's hard for him."