Bill Gates is still America's richest person, topping the list for the 20th time, after seeing his fortune soar to $72bn (£45.3bn).
The Microsoft founder's $6bn surge in wealth over the year saw him overtake Mexican telecoms tycoon Carlos Slim as the world's richest person in May, after the value of his share holdings in Microsoft soared.
Warren Buffett, boss of Berkshire Hathaway, came in second place after gaining $12.5bn, which rose to $58.5 bn, according to Forbes' latest list of the 400 richest Americans.
Oracle co-founder Larry Ellison is at third, with a $41bn fortune. However, he did not see his net worth grow over the year.
Only 30 of those on the rich list have got poorer since 2012, with everyone listed worth more than $1.3bn.
Christy Walton, who is the richest woman in the world and part of the Walmart supermarket dynasty, is sixth on the list with a fortune of $35.4bn.
Facebook founder Mark Zuckerberg saw his fortune rise $9.6bn to $19bn, meaning the social network boss is now at 20th place.