Three days of heavy rain have prompted the US National Weather Service to issue flood and flash flood warnings from Texas to Pennsylvania.
Worst hit are Missouri, Arkansas, Illinois, Ohio and Kentucky.
The US Coast Guard has helped rescue people trapped in their homes and cars.
Hundreds of people have been evacuated from their homes.
Roads have become totally impassable in many areas.
The authorities say a big problem has been people driving into floodwater.
Areas at risk of flooding have been constructing defences.