From the U.S. Census:
The U.S. Census Bureau reports that five of the counties or county-equivalents nationwide with the highest median household income in 2012 were located in Northern Virginia. Among them were Arlington County, at $99,255, Fairfax County, at $106,690, Falls Church (an independent city), at $121,250, Loudoun County, at $118,934, and Stafford County, at $95,927. Falls Church and Loudoun also had among the lowest poverty rates in the country.
The data are from the Small Area Income and Poverty Estimates program, which provides the only current, single-year income and poverty statistics for all sizes of counties and school districts ─ roughly 3,140 counties and nearly 14,000 school districts nationally.
The findings also show that median household income is higher in nearly half of the counties in the Dakotas now than it was before the recession began in 2007. Between 2007 and 2012, 55 of the 119 counties in North and South Dakota experienced a statistically significant increase in median household income. In contrast, of the remaining 3,023 counties or equivalents nationwide, the same was true of only 56 of them. Of all the U.S. counties with a statistically significant change in income relative to 2007, 89 percent experienced a decline.
Among the counties with school-age child poverty rates significantly higher than the national average of 21.1 percent in 2012, 75 percent were in the South. In 2012, there were 13,544 school districts. Of these, 14.7 percent had poverty rates greater than 30 percent, for the population of school-age children in families.