The number of affluent individuals in the United States is growing rapidly, according to a recent analysis by the Spectrem Group, a Chicago-based consulting firm. The number of millionaires rose 11 percent in 2005, but the ultra-high-net-worth group—those Spectrem defines as having a net worth of $5 million or more, excluding their primary residence, surged 26 percent to a new record of 930,000, the firm reported.

"Clearly, the stock market, which posted solid improvement in 2005, was one reason for the advance," Catherine S. McBreen, managing director of Spectrem, says. "However, for the wealthiest Americans, it appears the increased use of international markets and alternative investments were key drivers of their improvement."

Spectrem's report, Affluent Market Insights 2006, shows that affluent households continue to hold the largest percentage (45 percent) of their wealth in financial assets, including stocks and bonds, managed accounts, IRAs, mutual funds and alternative investments. Privately held businesses account for 15 percent, followed by their principal residence (14 percent), pension and defined contribution plans (11 percent), other real estate (9 percent), insurance and annuities (5 percent) and restricted stock (1 percent).

The report is based on data gathered through mail and online surveys of 1,014 qualified respondents from September to November 2005.