3. Mississippi River, 1927 – $3.2 to $4.5 billion
When the Mississippi flooded in 1927, it didn’t cause as much financial damage as it would in later flooding, but it claimed more than 250 lives and left more than 1.5 million people homeless. The Mississippi stayed at flood level for 153 days, and powerful waters broke at least 100 levees. The waters spilled over parts of Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee. A Risk Management Solutions study, published on the 80th anniversary of the flood, estimated that a repeat of the same flood would cause up to $160 billion in damages in modern times.