The number of U.S. households with a net worth of at least $1 million rose for the third consecutive year in 2005 to a record 8.9 million, according to a report by TNS Financial Services, a British market research firm. In 2004, there were 8.2 million households in this group. The firm also released a list of the 10 U.S. counties with the highest concentration of millionaires. Heading the list are: Los Angeles County, (262,800 millionaire households); Cook County, Ill. (167,873); Orange County, Calif. (113,299); Maricopa County, Ariz. (106,210); and San Diego County (100,030).

The average millionaire household has a mean net worth of $2,167,167 (excluding the value of primary residences), with mean investible assets of $1,442,841. The steady rise in millionaire households is the result of long-term wealth accumulation. Seventy percent of the households own stocks and bonds, 68 percent are in mutual funds and 58 percent invest in IRAs.

Although 73 percent of those surveyed preferred to do all of their financial business with a single institution, very few actually do. Six in 10 households receive investment advice from a professional advisor. Nearly 45 percent of the heads of millionaire households are retired, with a median age of 58. Maintaining a comfortable standard of living during retirement topped protecting and preserving estates, improving household liquidity and charitable giving as the chief financial goal of millionaire households.