The combined net worth of the 2012 class of the 400 richest Americans is $1.7 trillion, up from $1.5 trillion a year ago. The average net worth of a Forbes 400 member is a staggering $4.2 billion, up from $3.8 billion, and the highest ever, as two-thirds of the individuals added to their fortunes in the past year.

The top 12 richest Americans in 2012 take picture together. [Forbes.com]

The followings are the top 10 richest people in America of 2012:

   Michael Bloomberg

 

Michael Bloomberg [Forbes.com]

Net Worth: US$25 billion

Age: 70

Source of Wealth: Bloomberg LP, Self-made