NEW YORK (CNNMoney) -- Defining "rich" is always subjective.
But the IRS took a stab at it on Friday in a treasure trove of new personal wealth data from 2007 -- the most recently available.
The finding: An estimated 1.8 million Americans had a net worth of at least $2 million. That's a 12.1% increase over 2001.
As a group, the high-net worth club's combined net worth -- total assets minus debt -- was $11.6 trillion.
Not everyone was a Buffett-aire, however.
More than half of the 1.8 million had a net worth between $2 million and $3 million.
And only 66,000 had a net worth of $20 million or more. These ultra-rich individuals had a combined net worth of nearly $4 trillion, or one-third of the combined net worth of the larger group.
The most commonly held assets among high-net-worth individuals? Real estate, stocks and various retirement assets such as IRAs and annuities.
Of course, not all states are created equal when it comes to the high-net-worth crowd.
California took the prize for most residents worth $2 million or more -- 329,000; they had a combined net worth of nearly $2 trillion. New York ranked a distant second with 160,000 wealthy residents who had a combined net worth of $1.2 trillion.
Meanwhile, Wyoming took the No. 1 spot for having the greatest concentration of wealthy residents: 6,000, representing 1.5% of the state's total adult population.
Connecticut came in second, with 36,000 high-net-worth residents representing 1.3% of its adult population.
The IRS, which updates its personal wealth data every three years, based its findings on estate tax returns filed in 2007, 2008 and 2009.
Estate tax returns offer the most complete picture of one's total wealth since they include a complete listing of one's assets and debts, the IRS said. The IRS treats the estate tax returns as a random sampling of wealth held by those still living.
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