One of the most exclusive clubs in the U.S. has picked up more members.

About 47,000 people had a net worth of $20 million or more in 2004, the latest available year, according to new estimates by the Internal Revenue Service. While that was up only slightly from 46,000 in 2001, it was up 62 percent from 29,000 in 1998.

The IRS also reported increases in the number of people with a net worth between $10 million and $20 million: 79,000 people qualified for this group in 2004, up from 77,000 in 2001 and 51,000 in 1998.

California had the largest number of residents with a net worth of $1.5 million or more, with 428,000 in 2004. Florida came in second, with 199,000, followed by New York (168,000), Texas (108,000), Illinois (101,000), Pennsylvania (86,000) and Massachusetts (83,000).

This new peek inside the nation's upper crust comes from IRS data posted recently on the agency's Web site (irs.gov). While nobody knows precisely how many millionaires or multimillionaires there are, the IRS figures are considered an important indicator, since they're based on federal estate-tax returns, which include extensive details on assets and debts of wealthy people who have died. IRS analysts use data on these returns to estimate the wealth of the living.