More than 2,300 flights were canceled and more than 3,500 delayed, majority out of Chicago's O'Hare International and Midway International airports, according to the flight tracking site FlightAware.com.
Natural gas supplies were under threat in MI and Minnesota.
Natural gas supplies were under threat in MI and Minnesota, where authorities asked residents to reduce their heat consumption if at all possible. Elsewhere, a man was struck by a snowplow in the Chicago area, a young couple's SUV struck another on a snowy road in northern in and a Milwaukee man froze to death in a garage, authorities said.
Amtrak began to restore service out of Chicago, one of the nation's busiest rail hubs, after canceling dozens of trains.
"We are not done yet".
Local television pictures showed the Chicago River and Lake Michigan filled with chunks of ice.
Air masses drifting further south than usual are pushing wind-chill temperatures to dangerously low levels: Cold enough to cause frostbite in half an hour.
Tens of millions of Americans braved Arctic-like temperatures as low as minus 56 degrees Fahrenheit (minus 49 Celsius) on Thursday that paralyzed the US Midwest and were blamed for at least 21 deaths.
The weather service initially hinted of a possibility that Thursday morning could shatter the 1985 record.
On Wednesday night, Consumers Energy, one of the main energy providers in MI, sent out an emergency appeal to customers throughout the state to reduce their heat as much as possible to avoid a critical gas shortage.
Frostbite could be possible within 10 minutes of exposure to the extreme weather, the National Weather Service has warned.
America's northern neighbour Canada was also contending with extreme cold, with frozen water pipes and snarled travel on a major waterway.
Officials warned Chicago residents to expect a potentially deadly and unsafe freeze. More than 1,000 USA flights have also been delayed.
Multiple warming shelters were opened Monday by agencies and nonprofit groups across the Midwest and Northeast to get the homeless population off the streets. This morning, Chicago reported wind chills of negative 52 degrees, while Iowa described wind chills of negative 42 degrees.
While officials warned residents to remain on guard as long as the sub-zero weather persisted, authorities in MI and Minnesota were also asking them to turn down their thermostats to conserve natural gas. The warning followed a fire at a utility's suburban Detroit facility that affected natural gas supplies.
"This is not over until noon tomorrow".
Michigan Governor Gretchen Whitmer said government offices would remain closed through Thursday.
General Motors Co suspended operations at 11 MI plants and its Warren Tech Center after a utility made an emergency appeal to users to conserve natural gas after extreme cold and a fire at a compressor station.
City crews braved sub-zero weather to fix a number of frozen water main breaks that plagued Motor City neighbourhoods.
Chicago reported 22 broken water mains, 16 of which had already been repaired. A 70-year-old man was found Wednesday frozen to death outside a neighbor's house in Detroit, where the high temperature barely reached -2 Fahrenheit.