But the top ten rankings remained unchanged, with Microsoft founder Bill Gates holding the number one spot for the twentieth consecutive year.
Gates, whose net worth has risen $6bn to $72bn over the last year, in May overtook the Mexican telecoms billionaire Carlos Slim to reclaim his position as the world's richest man.
In second place, Berkshire Hathaway investor Warren Buffett closed the gap with Gates by increasing his net worth by $12.5bn to $58.5bn, making Buffett the year's biggest dollar gainer.
Larry Ellison, the founder of software company Oracle, sticks at $41bn in the number three spot, while the joint fourth-richest Americans are Charles and David Koch, the brothers behind the sprawling global conglomerate Koch Industries, who each have a $36bn fortune, up from $31bn each last year.
Collectively, the 400 richest Americans have finally gained back their losses from the financial crisis.
The minimum net worth needed to make this year's list is $1.3bn the highest entry point since property and stock market values crashed in 2008.
The combined net worth of the 400 richest Americans has risen $300bn to a record $2trn, comparable to the GDP of Russia. The raised bar for entry means that 61 US billionaires fall outside the top 400.
The average net worth of the members of the Forbes 400 is $5bn, the highest to date, up from $4.2bn last year. Net worth has increased for 314 members of the top 400, and decreased for 30 members.
Notable newcomers to Forbes' wealth rankings include Michael Rubin, the founder of the online sports retailer Kynetics, at 243, and Robert Pera, the head of the wireless technology manufacturer Ubiquiti Networks, at 293.
Pera, 35, is one of the nine businessmen under 40 on the Forbes list.
The biggest percentage gainer is David Duffield, the 72-year-old co-founder of the software business Workday, whose fortune has more than tripled to $6.4bn after the company's IPO last October.
The Forbes rankings are based on a snapshot of wealth taken on August 23.