24/7 Wall St. compiled a list of the worst floods in U.S. history by the number of fatalities. Floods occur for various reasons — dams bursting, intense rainfall, massive water runoff from snowmelt, storm surge from hurricanes, even impact from tornadoes. In order to capture the scope of these tragic historical chapters in our nation’s history, we tried to include any and all weather-related events that could have contributed to floods. 24/7 Wall St. used government sources such as the National Weather Service Weather Forecast Office, The National Oceanic and Atmospheric Administration, and the United States Geological Survey as well as media reports about the flood events to create a list of the worst floods in U.S. history. The cost of damage was rendered in inflation-adjusted dollars.