Richest Neighborhood in USA - Greenwich, CT

Sorry, New York and California. The state with the richest neighborhoods is little ole' Maryland.

A new ranking of the 100 richest neighborhoods in America finds that three of the top five are in Maryland, all of them close to Washington, D.C.

This follows another recent study that found that Maryland also has the highest population of millionaires per capita than any other state, suggesting that the D.C.-area is becoming one of the nation's leading centers of wealth.

The new neighborhood list, called the Higley Elite 100, is compiled by Stephen R. Higley, professor emeritus of urban geography at the University of Montevallo in Alabama. The list ranks neighborhoods--rather than ZIP codes or cities--by mean household income and census data, and is based on the Census Bureau's "American Community Survey 2006-2010."

Higley said that since the census income measure tops out at $2 million, it doesn't give more credit to the super-rich earners. That could lower the rankings for neighborhoods in New York, Los Angeles and San Francisco.

(Read more: Which state leads in millionaires per capita?)

Still, the list is a good measure of overall affluence--if not superwealth.

Ranking first on the list is the "Golden Triangle" in Greenwich, Conn., which includes homes for many of top hedge funders. The mean household income in the triangle is $614,242. Higley said the average asking price of a home in the "Triangle" was $6.7 million.

Ranking second was the Bradley Manor-Longwood enclave of Bethesda, Md., with a mean household income of $599,440, followed by Potomac Manors in Potomac, Md., with $599,331. Another Potomac hood, Carderock-The Palisades, came in fifth, with $595,669.

Other neighborhoods near D.C. also ranked high, including the Swinks Mill-Dominion neighborhood in McLean, Va.,(ranking 7th) and the Glendale area of McLean (ranked 19th).

(Read more: How to become a millionaire? The answer's changed)

Some say the rise in wealth in D.C. is a sign of the growth in the "business" of Washington, like lobbying and contractors. But Higley said it's more a sign of the rise of dual-earners in D.C.

"In Maryland and Virginia, you have all these double-professional families," he said. "They may be making $300,000 or $400,000 a year. But they're not rich in the way that you'd find in New York or Los Angeles."

The Golden Triangle bumped off the previous No. 1 on the list, Holmby Hills, Calif. But Higley said Holmby's fall was due mainly to a redrawing of the neighborhood to include an area with condo towers.

"Nothing kills a high ranking like condo towers," he said.

Higley said the study also shows the increasing diversity of today's rich neighborhoods. He said Asians and Latinos have gained the most. The white population of America's highest-earning 1,000 communities has fallen to 83 percent from 91 percent in 2000, he said. In some rich neighborhoods, the decline is far more substantial.

(Read more: Born in San Fran? Your ladder is easier to climb)

The Old Cutler-Hammock neighborhood of Coral Gables, Fla., ranked fourth on the list, with a mean household income of $596,851. Fully 48 percent of the neighborhood's population is Latino. Higley said that roughly two-thirds of the Latinos are Cuban--mostly business owners or entrepreneurs, many of whom were wealthy in Cuba before emigrating.

"Even in the richest neighborhoods, the demographic change is substantial," he said.

Here are the 10 most affluent neighborhoods in America, as measured by mean household income.

--By CNBC's Robert Frank. Follow him on Twitter @robtfrank.