Those fatalities in Woodward are the only ones known to have resulted from this weekend's storms. But millions of people were bracing for even more severe weather late Sunday afternoon and night.
The states in the "bull's-eye" for the most dangerous conditions Sunday will likely be Wisconsin, Minnesota and Iowa, according to the Storm Prediction Center. CNN Meteorologist Alexandra Steele added that some bigger cities -- including Green Bay, Chicago, St. Louis, Little Rock and Houston -- could see isolated tornadoes, large hail and damaging winds.
About 5 million people from Wisconsin to Texas "need to be on guard," Steele said.
The National Weather Service received 122 reports of possible tornado touchdowns Saturday and early Sunday in Oklahoma, Kansas, Nebraska and Iowa.
Kansas Gov. Sam Brownback told CNN that "97 tornadoes touched down" in his state; the National Weather Service has not confirmed the exact number of twisters.
Oklahoma Gov. Mary Fallin declared a state of emergency for 12 counties, including Woodward, where the deaths occurred.
Up to 250 emergency responders came into the small city of Woodward, conducting a door-to-door search to ensure there were no more fatalities, said City Manager Alan Riffel.
Mayor Roscoe Hill said 37 people were injured, including several critically, when the storm struck the northern Oklahoma community -- which has about 12,000 people, in a county of 20,000, and sits about 85 miles west of Enid -- shortly after midnight. Matt Lehenbauer, director of emergency management for Woodward, said 29 people have been treated for injuries.
"This thing comes in the middle of the night. It caught us asleep, mostly," Hill told CNN.
In addition to leveling 89 homes and 13 businesses, Riffel said the storm "took out" the transmitter for the public siren and tornado notification system, and "we lost our manual override" when the electricity was knocked out.
"We don't know if it would have saved those killed, but I'm sure we could have woke people up with sirens if they were working," said Hill.
The dead includes a father and his two children, who were inside their trailer at the Hidden Valley Mobile Home Park when the tornado rolled through, according to Hill.
The other two people killed were in a car that rolled over several times.
"It's hard to visualize" such a tragedy, Hill said.
Officials credited working early warning systems elsewhere in the region with preventing more fatalities.
Advisories from the system were issued two days in advance, rather than just a matter of hours, and were "remarkably accurate," said Brownback, the Kansas governor. "People took it very seriously."
In southwest Iowa, officials evacuated the entire population -- roughly 300 people -- of the town of Thurman after a suspected tornado struck Saturday, damaging or destroying three out of every four homes.
By early Sunday morning, many Thurman residents who took up temporary shelter at a high school in nearby Tabor were again in the path of a storm that spawned suspected tornadoes in neighboring Kansas.
A sign in a park that bears the town's name is one of the few things still standing, said Mike Crecelius, Fremont County's emergency management director.
"That's about all there is. About 75% of the homes are damaged or destroyed," he said. "From the looks of things, there won't be a tree left in that town either."
Across the south and central Plains, storm chasers broadcast images of funnel clouds roaring through rural landscapes.
In the basement of 30-year-old Lacy Jay Hansen's home in downtown Wichita, Kansas, she and her family donned bicycle helmets and crouched against a corner as a suspected tornado churned its way toward her home.
"It turned right in the nick of time for us, striking this other neighborhood," she said, later learning the storm destroyed a friend's house several miles away.
Eleven months ago, Hansen, her husband and son were in Joplin, Missouri, visiting their ailing grandfather in a hospital when a tornado ripped through, killing 158 people.
"None of us were supposed to be there," she said. "We've always taken it seriously. But ever since then, we take it more seriously."
The tornado that tore through Joplin was one of 1,691 tornadoes that killed a total of 550 people in 2011, according to the National Weather Service. Last year was the 4th deadliest tornado year in U.S. history.
The tragedy in Joplin triggered stronger warnings by the weather service about life-threatening storms. More than 24 hours before the storms began rolling across the Midwest on Saturday, the service was cautioning residents of the storm's potential damage.
At the Marriott in downtown Wichita, Johnny Williams watched over eight children in an interior ballroom where they'd taken shelter.
The group, from Oklahoma City, was in town for a basketball camp at the time
"We play together as a team, and we believe together as a team," Williams said. "We really believe everything will be all right."
The storm caused flooding in parts of downtown Wichita, and McConnell Air Force Base also sustained damage, authorities said.
Wichita resident Katie Sykes sent CNN iReport a photo of what she called "the river in my front yard."
"About midnight I was in my basement, and I come upstairs and I see the water -- it looked like a river,' she said.
"When I was little we prepared for storms, hearing the sirens and then going to the basement. And going through this experience I felt like a little kid, young and scared."
A roof collapsed at a facility for Spirit Aero Systems, which produces fuselages and other equipment for Boeing aircraft, and damage was also reported to a Hawker Beechcraft building, which manufactures high-performance business jets and turbo-prop planes.
At the Wichita Mid-Continent Airport, a suspected tornado tossed baggage carts across runways, Sedgwick County spokeswoman Kristi Zuckovich said. There was no structural damage and the airport was fully operational Sunday, she said.
Country singer Miranda Lambert's concert Saturday night at the Intrust Bank arena in Wichita was interrupted by an apparent tornado. She was taken off the stage and fans were kept inside, said Lt. Jason Gill of the Sedgwick County Sheriff's Office.
Later, Lambert tweeted, "We made it y'all. Thanks for coming out and for making it through the delay with a smile."
Six mobile homes were destroyed in Wichita County, officials said. Authorities searched Sunday morning to be sure everyone was accounted for.
Earlier, a confirmed tornado struck a hospital in Creston, Iowa, blowing out windows and damaging the roof, said John Benson of the Iowa Homeland Security and Emergency Management agency. There were no major injuries reported, and patients were relocated to other area hospitals.
