More than 1.5 million people lost power and thousands of flights were cancelled on Friday.
The vast storm extends more than 2,000 miles (3,200km) from Texas to Quebec.
A bomb cyclone, when atmospheric pressure plummets, has brought blizzard conditions to the Great Lakes on the US-Canada border.
In Canada, Ontario and Quebec were bearing the brunt of the Arctic blast, with power cut to hundreds of thousands.
Much of the rest of the country, from British Columbia to Newfoundland, was under extreme cold and winter storm warnings.
The US National Weather Service (NWS) said its Friday map "depicts one of the greatest extents of winter weather warnings and advisories ever".
Temperatures in Elk Park, Montana, dropped to -50F (-45C), while the town of Hell, Michigan, has frozen over.
It was 1F (-17C) in the snow-covered community on Friday night. Emily, a bartender at Smitty's Hell Saloon, told the BBC: "It's pretty cold here, but we're having a hell of a time."
In South Dakota, snowed-in Native Americans burned clothes for warmthafter running out of fuel, said tribal officials.
Heavy snowfall was forecast in areas of Pennsylvania and Michigan. Buffalo, New York, was expecting at least 35in (89cm). More than eight million people remained under blizzard warnings, said the NWS.
Coastal flooding has been seen in New England, New York and New Jersey.
In the Pacific Northwest, some residents ice-skated on frozen streets in Seattle and Portland.
Even the usually milder southern states of Louisiana, Alabama, Florida and Georgia were experiencing hard-freeze warnings.
A number of the storm-related fatalities have involved road traffic accidents, including a 50-car pile-up in Ohio that killed two motorists.
Travel problems across the country were being exacerbated by a shortage of snow plough operators, with low pay rates being blamed.
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