From New York and Massachusetts in the northeast to Texas and North Carolina in the south, roads were frozen slick with ice and buried under snow.
At least 25 governors declared states of emergency.
In some southern US states, residents faced winter conditions unseen for decades, with 2.5cm-thick ice bringing down trees and power lines.
The storm was blamed for at least 18 deaths across multiple states.
In Frisco, Texas, a 16-year-old girl died in a sledding accident on Sunday; another youth died in Saline County, Arkansas while being pulled by an ATV vehicle over snow and ice when it struck a tree, authorities said.
In Pennsylvania, three people died while shovelling snow, local media reported.
In Austin, Texas, a person died of apparent hypothermia while trying to shelter at an abandoned service station, authorities said.
At least five people died in New York City from exposure to the cold, Mayor Zohran Mamdani said on Sunday, urging residents to call for help if they saw anyone out on the street in need.
While the storm system was drifting away from the east coast into the Atlantic on Monday, a blast of Arctic air was rushing in from Canada behind it, prolonging sub-freezing temperatures for several more days, the National Weather Service said.
"This storm is exiting the east coast now, with some lingering snow squalls," said Allison Santorelli, a meteorologist with the NWS's Weather Prediction Center.
"But the big picture story is the extreme cold, it's lasting into early February."
Almost 200 million people across the US were under some form of extreme cold alert, from along the Canadian border to the Gulf of Mexico, forecasters said.
Lubbock, Texas, had a low of minus 20C on Monday and New York City, Washington DC. and Boston all faced single-digit temperatures through much of the week ahead.
Nearly 800,000 customers, including both homes and businesses, across the southeastern US were facing the cold weather without power, according to the tracking site PowerOutage.us, including 246,000 in Tennessee.
