Millionaires add to their ranks

They're moving on up.

The number of millionaire households rose by 200,000 to hit 8.2 million in 2011, according to new research by the Spectrem Group. These folks had at least a million dollars in assets, not including their primary residence.

Though their ranks have been expanding for three straight years, there are still fewer millionaires in the U.S. than there were before the Great Recession. In 2007, millionaires numbered 9.2 million.

Millionaires are not the only ones whose numbers have failed to hit their pre-recession highs.  Those with $500,000 in assets rose to 13.8 million last year, but still don't come close to their peak of 15.7 million in 2007.

The richest of the rich -- those with at least $25 million in net worth -- edged up to 107,000, but remain below their 2007 high of 125,000.

Despite the bullish stock market, millionaire investors remain concerned about holding onto their wealth. Close to 60% are worried about maintaining their financial position, while more than half worry about a family health catastrophe, college costs and the financial well-being of their children and grandchildren.