Thanks to the strength of the U.S. stock and real estate markets, many members of this elite club have regained the wealth they lost several years after the global economic crisis. Collectively, the Forbes 400 is worth more than ever -- a record $2 trillion.
Microsoft co-founder Bill Gates, who has pledged to give away more than half of his wealth, earned the top spot on the list for the 20th year in a row, just months after he surpassed Mexico's Carlos Slim to become the world's richest person.
Warren Buffett came in second with $58.5 billion, while the Koch brothers came in third and fourth with $36 billion each.
Facebook co-founders Mark Zuckerberg and Dustin Moskovitz are the youngest Americans on the list, with $19 billion and $5.2 billion respectively.
Here are the top 10:
1. Bill Gates $72 billion
2. Warren Buffett $58.5 billion
3. Larry Ellison $41 billion
4. Charles Koch $36 billion
5. David Koch $36 billion
6. Christy Walton & family $35.4 billion
7. Jim Walton $33.8 billion
8. Alice Walton $33.5 billion
9. S. Robson Walton $33.3 billion
10. Michael Bloomberg $31 billion
You can read the full list here.