The number of extremely rich people living in the United States declined by 18.5 percent in 2008 as the economic crisis took hold, according to a new report.

Capgemini, which provides consulting, technology and outsourcing services, released its new annual Metro Wealth Index this week. It measured the number of people with more than $1 million dollars in investable assets excluding primary residence and showed that big cities fared better than the nation as a whole.

In total, the number of super-rich in the top ten U.S. metropolitan areas declined by 15.7 percent, or nearly 300,000, with New York faring by far the best, followed by Los Angeles and Chicago.

New York's rich fell by 13.6 percent to 561,800, the index said, with Los Angeles falling 17.8 percent to 208,200 and Chicago falling 16.2 percent to 172,200.

This index shows where the wealth is residing and it also shows where it is shifting, said Ileana Vander Linde of Capgemini's Wealth Management division.

The list showed that areas with growing populations had not necessarily gone up the index, as certain cities had been hit by the property crash at the epicenter of the financial crisis.

Cities like Phoenix and Orlando, areas that have seen large general population increases in recent years, lost more than 30 percent of their mega-rich population.

It has a lot to do with the industries that back up those cities. Huge dependence on real estate in those cities means they have been affected a lot more severely, Linde said.

Conversely, cities with a wider variety of industries have fared better through the crisis, according to the index.

San Francisco, San Jose and Boston, while also suffering declines, were in the top ten for rich numbers.

Other cities are more dependent on other industries -- technology, governmental services -- so if you look at the top ten we have San Francisco, San Jose, Boston. They have suffered less, Linde said.

(Reporting by Edward McAllister; editing by Patricia Reaney)