NEW YORK (CNN/Money) - Microsoft Chairman and co-founder Bill Gates once again topped the list of richest Americans, even though his net worth tumbled some 20 percent over the last year, along with the sinking stock market, to $43 billion.

Gates remained ahead of famed investor Warren Buffett, whose $36 billion fortune put him at No. 2, according to Forbes' list of the 400 wealthiest Americans, to be published in the Sept. 30 issue of the magazine.

Bill Gates

Microsoft co-founder Paul Allen came in third with a net worth of $21 billion.

The heirs of Sam Walton, who founded Wal-Mart Stores (WMT: Research, Estimates), occupy the fourth through eighth spot, each with a net worth of $18.8 billion.

The rich, like almost everyone else over the last year, got a little less rich. The total net worth of those on this year's list is $872 billion, $74 billion less than last year.

That marks just the fourth time in 20 years that the combined wealth of the richest Americans fell, Forbes said.

Microsoft (MSFT: Research, Estimates) shows up again in the No 10 slot. Steve Ballmer, the software maker's CEO, has a fortune worth $11.9 billion, Forbes said.

At No. 9, Oracle's (ORCL: Research, Estimates) Larry Ellison tops him with a $15.2 billion.

Most of the people occupying top spots have their money in stocks. So it's no wonder that the average net worth fell during a year when the Standard & Poor's index of 500 companies is down more than 22 percent.

The youngest, Daniel Ziff, 30, has an inherited fortune of $1.2 billion. The oldest investor is Max Martin Fisher, 94, with $750 million.

There are 46 women on the list, including Meg Whitman, the head of eBay (EBAY: Research, Estimates). Her $780 million in net worth put her 300th on the list. Oprah Winfrey is 229th with $975 million.

Martha Stewart was among 35 people bumped, largely because her company's stock tumbled after her legal troubles.

The "poorest" members of the Forbes 400 have a net worth of $550 million. Gary Winnick, the head of bankrupt Global Crossing, is among them, dropping from 277th last year. A congressional committee this week subpoenaed Winnick to answer questions about the struggling company.  

-- from staff and wire reports