The Washington area's affluence and education levels make it the wealthiest and most educated region in the nation, according to census data released Tuesday that reflect five years of relative prosperity compared with the rest of the country.

During that period, Fairfax and Loudoun were the only two U.S. counties with median household incomes surpassing $100,000. Tiny Falls Church, which is an independent city and counted separately, had that median income level, as well. Five of the region's suburban counties - Fairfax, Arlington, Loudoun, Montgomery and Howard - plus Alexandria and Falls Church, were among 17 places in the United States in which more than half of the residents have at least a bachelor's degree.

In Loudoun, more than a third of the households are married couples with children, making it one of the country's bastions of the traditional family. The District, Baltimore and Richmond reflected the other extreme, with nuclear families making up fewer than one in 10 households.

The census data released Tuesday offer a more intimate glimpse of hundreds of the Washington region's neighborhoods than has been available. Among other things, the data will be used to provide a better understanding of segregation in the area and other U.S. communities.

The figures combine information gathered from 2005 to 2009 in the American Community Survey, a detailed questionnaire mailed monthly to a cross section of Americans.

The estimates were among 11 billion statistics made available in what Census Bureau Director Robert M. Groves called the biggest release of data "in the history of mankind" for 670,000 geographical units, including school districts and census tracts. It encompasses boom times, the descent into recession and the first inklings of recovery.

William Frey of the Brookings Institution has started to mine the data, concluding that segregation is declining nationally and locally. In his analysis of the 100 largest metropolitan areas, 61 experienced declines in segregation between blacks and whites.

In Washington, Frey found that the average white person lives in a neighborhood that is 63 percent white, the average black person lives in a neighborhood that is 79 percent African American and the average Hispanic person lives in a neighborhood in which one out of four neighbors is Hispanic. That represents a small but noticeable improvement since 2000.

The District exhibited the most segregation overall under a measurement called the Index of Dissimilarity or, more commonly, the segregation index. It estimates what percentage of people would have to move for races to be distributed in the same proportion in which they're represented overall in a region, with zero being the ideal and anything more than 60 considered high.

At 74 percent, the District had the fifth-highest segregation level in the nation, and Virginia had one of the lowest, 50 percent. Maryland was in between, with 65 percent.

Frey said that the District and Virginia had fewer residents living in segregated neighborhoods than in 2000 but that Maryland was unchanged. He attributed the improvement to the maturation of the civil rights movement and laws prohibiting discrimination in housing.

"I anticipate that in the 2010 Census we will see results that are similar," he said.