America’s Richest Zip Codes 2011 - No. 1 Richest Zip Code: 33480, Palm Beach, Fla. -

America’s Richest Zip Codes 2011 - No. 1 Richest Zip Code: 33480, Palm Beach, Fla. - 

It should come as no surprise that rich people like living around other rich people. From Shibuya in Tokyo and the Seventh Arrondissement in Paris to Manhattan’s Upper East Side and the tree-lined avenues of Palm Beach, Fla., wealth gravitates to wealth. As the global income gap between rich and poor widens, the richest neighborhoods keep getting richer—and bigger.

Take, for example, Palo Alto, Calif. Over the last decade, hundreds of wealthy people have relocated to this university town as local Silicon Valley tech businesses boomed. It is home to such companies as Facebook, Hewlett-Packard (HPQ), and VMWare (VMW). Thanks to so much new money, Palo Alto‘s 94304 zip code is one of the fastest-growing pockets of wealth in the U.S. The number of households in this area, where the average household net worth is $1.3 million, more than doubled since 2000, according to data from Little Rock (Ark.)-based Gadberry Group.

While many zip codes in the U.S. have been battered by the economic downturn, neighborhoods around Palo Alto are among a small group of expanding rich areas. In a new OECD report, the top 10 percent of the country’s income earners made nearly 15 times more than the bottom 10 percent in 2008, up from a multiple of 12 in the mid-1990s. As is often the case, the rich are grouping near golf courses, beaches, upscale boutiques, and schools.

So where are these privileged zips? In an exclusive analysis for Businessweek.com, Gadberry Group identified the 100 richest zip codes in the U.S., based on average household income and average household net worth. The survey included only places with more than 100 households. (Of the top 50 locations we profiled from Gadberry’s list, the zip with the least number of households is in Mill Neck, N.Y., and the biggest lies in Potomac, Md. The number of households in the 100 richest zip codes—which have an average household net worth of $1.4 million—grew by 7.4 percent from 2000 to 2011, based on Gadberry’s data. (Click here to see the richest, growing zip codes in the U.S.)

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