Millionaires on the rebound

NEW YORK (CNNMoney) -- What recession? The millionaire population jumped in the U.S. by 8% last year, fueled by the stock market recovery, according to an industry report on Wednesday.

The number of U.S. households worth at least $1 million rose to 8.4 million in 2010, compared to 7.8 million the prior year, according to a report by Spectrem Group.

"The affluent market grew in 2010 due primarily to the stock market rebound, but despite their growing portfolios, attitudes remain significantly different than in 2007," the report said.

"The size of the affluent market increased in 2010 but did not reach the highs obtained in 2007," the year that the recession began, according to the report.

Last year marked the second consecutive year of increases, the group said, following a 16% surge in the millionaire population in 2009.

"The millionaire comeback continues," said George H. Walper Jr., president of Spectrem Group.

But he added that many millionaires are still operating under a cloud of caution.

"While investors are feeling positive about their own portfolios, they are not convinced that the economy has recovered," said Walper. "Our ongoing polling and research indicates that investors remain unconvinced that we are back on solid ground."

In the prior year of 2008, the millionaire population plunged 27%.

The group said the number of "ultra high net worth" households, with a net worth of at least $5 million, jumped 8% in 2010 to 1.06 million, compared to 980,000 the prior year.

The broader affluent population, meaning households with a net worth of $500,000 or more, also grew in 2010. This population rose by 6% to 13.5 million in 2010, compared to 12.7 million the year before.

Households worth at least $100,000 also grew last year, to 36.2 million from 34.6 million. But the report showed that Americans, even those with money, are more cautious than they used to be.

"Overall attitudes are not the same as in 2007," the report said. "Many households no longer believe their home is a stable asset."

The report also showed that 55% of households worth less than $1 million "still feel that it is more important to protect their principal than grow their assets."