Below Gates, there was no change to the top 10, with Jeff Bezos, Warren Buffett, Mark Zuckerberg, Larry Ellison, Charles and David Koch, Michael Bloomberg, Larry Page and Sergey Brin all holding their places - each of them getting at least US$1b richer.
The biggest gainer (in dollar terms) was Facebook's Mark Zuckerberg, whose fortune jumped US$15.5b. However, despite the jump, Zuckerberg could only retain his spot as fourth richest American from last year.
The list also featured 289 gainers since last year, outnumbering losers (just 51) by more than five to one.
There were 22 newcomers on the list. Among the most notable were: Arizona iced tea co-founder Don Vultaggio, Netflix co-founder Reed Hastings, Tito Beveridge, the creator of Tito's Handmade Vodka, Chuck Bundrant, whose Trident Seafoods sells fish to places like McDonald's and Burger King, and Rocco Commisso, founder of cable TV and broadband firm Mediacom and owner of the New York Cosmos, a football club based in Brooklyn.
The most notable loser was President Donald Trump, whose fortune fell US$600 million, dropping him from 156th place to 248th.
Twenty-six members of the 2016 list dropped out, most notably Under Armour's Kevin Plank, whose fortune fell to US$1.7b, down from US$3b.
A staggering record 169 billionaires were too poor to make the cut, including well-known people such as activist investor Nelson Peltz and Facebook's Sheryl Sandberg.
German-born, New Zealand citizen Peter Thiel sits at 315 with a net worth of US$2.6b.
Click here to see the full Forbes 400 list.