The number of millionaire households in the nation increased by 8% in 2010, marking a second straight year of growth, according to Spectrem Group.

The rise follows a 16% jump in 2009 and a 27% decline in 2008, according to the Chicago-based company's Affluent Market Insights 2011 report.

The number of ultra-high-net worth-households with a net worth of $5 million or more also grew 8% in 2010, to 1.06 million from 980,000 a year earlier.

Additionally, the number of households with a net worth of $500,000 or more grew by 6% in 2010, to 13.5 million from 12.7 million.

"After taking a big recession-driven hit in 2008, the U.S. millionaire population staged a second straight year of growth in 2010, adding 600,000 new millionaires," said Spectrem Group President George H. Walper, Jr.