In Clarksville, Missouri, some 500,000 sandbags and more than 8,000 tons of sand and rock are being used to keep most of the floodwater at bay.
Mayor Jo Anne Smiley said the worst is over, but the city isn't out of the woods yet.
Volunteers from around the area played a key role in protecting the town.
"The only way this community in particular survives these kinds of events is volunteer help, because we've had more volunteers in town than we have people who live here," Smiley told affiliate KSDK. "And the people who live here are for the most part aged."
Missouri Gov. Jay Nixon declared a state of emergency last week after many areas of the state were stricken by flash flooding.
"The sustained periods of heavy rainfall (have) swollen creeks and streams and is pushing the Mississippi River over flood levels, endangering river communities," Nixon said.
Record floodwater on the Rock River is dampening the mood at Rick Wyffels' Christmas tree farm in Moline, Illinois.
"This is going to be bad," Wyffels told CNN affiliate WQAD. "This is the highest water I've ever seen down here."
The Wyffels family has farmed along the Rock River for more than 60 years. About a quarter of his crop is under water.
"We'll just have to wait and see whether these trees make it or not," he said.
Back in July, it was a different story for Wyffels as the region was locked in a drought. He lost some 900 trees in the parched soil.
The rain and flooding caused three deaths last week and a fourth Sunday, local authorities reported.
In DuPage County, Illinois, a body was found floating in Salt Creek last week, the local sheriff's office said. Authorities were working to identify it.
A woman in De Soto, Missouri, drowned last week after her vehicle washed off a road, KSDK reported.
Two fatalities were reported in Arcadia, Indiana. On Thursday, a 64-year-old man died after attempting to cross high water in his car. The water swept him off a roadway and dragged him downstream, the Hamilton County Sheriff's Office said.