NEW YORK (CNNMoney.com) - The number of American millionaires rose to a record level last year, and they're disproportionately located in four counties in California, according to an analysis released Tuesday.

Other states with counties that boast the highest number of millionaires across the country are Illinois, Arizona, Texas, New York, Florida and Massachusetts.

Number 5 in millionaires: San Diego County

The millionaires next door Ten counties across America with the highest number of millionaire residents. Rank  County  No. of millionaire households  1  Los Angeles County, CA  262,800  2  Cook County, IL  167,873  3  Orange County, CA  113,299  4  Maricopa County, AZ  106,210  5  San Diego County, CA  100,030  6  Harris County, TX  96,593  7  Nassau County, NY  78,816  8  Santa Clara County, CA  75,371  9  Palm Beach County, FL  69,871  10  Middlesex County, MA  67,552     Source:  TNS Financial Services

Nationwide, households with a net worth of at least $1 million excluding primary residences rose 8 percent to a record high 8.9 million, according to an annual report by TNS Financial Services, a market research and polling firm.

The firm's survey found that the millionaire households had an average net worth, excluding principal residence, of nearly $2.2 million, of which more than $1.4 million was in liquid, or investable, assets.

Their overall debt levels, meanwhile, fell by 8 percent, from $179,000 to $165,000.

Who's heading these households? TNS found the median age of the head of millionaire households is 58, and 45 percent are retired. Roughly 19 percent own in whole or part a professional practice or privately held business.

Over 50 percent of the millionaires surveyed said they had become more conservative in their investment approach over the past year. Their wealth is the result of long-term wealth accumulation.

Although real estate is not their sole source of wealth, it remains a staple for many. Forty-six percent of those surveyed own investment real estate like a second home or rental properties.

Seventy percent of the households, meanwhile, owned stocks and bonds, and 68 percent owned mutual funds.

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For more on the TNS survey's findings, click here.

For a look at millionaires in the making, click here.