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.