Loudoun County is once again the richest county in the U.S., according the latest Census Bureau estimates.
The county boasts a median household income just shy of $126,000, the tops in the nation.
Almost 10,000 Loudoun residents commute to D.C., while the vast majority find well-paid jobs in the county. Top local employers include Dulles Airport, Loudoun County Public Schools and the Department of Homeland Security.
Others are employed within the vast array of technology companies and at data centers.
While Loudoun takes the top spot, according to the 2015 Census Bureau estimates, half of the richest counties in America are within an hour of the District of Columbia.
In second place is the nearby City of Falls Church. Technically an independent city, Falls Church is considered by the Census Bureau to be equivalent to a county. More than 78 percent of Falls Church adult residents have a bachelor's degree or higher. Over 31 percent of residents there are employed by the government.
Other D.C. suburbs with high earnings include Fairfax and Arlington counties and Howard County in Maryland.
The wealth is not confined to older generations. In six of the 10 counties, the median age is between 37 and 39. The national median age is 37.8. The oldest county on the list is Hunterdon County, N.J., with a median age of 45, while the youngest is Arlington County, with a median of 33.9.
The poverty rates in most of the counties making the list are also low. In both Falls Church and Colorado's Douglas County, the poverty rate is 4 percent, compared to the national rate of 13.5 percent, with most counties on the list falling between 4 percent and 6 percent. Only Arlington County and Santa Clara County, California, had higher poverty rates, at 9 percent and 9.5 percent, respectively.
The Census Bureau's Small Area Income and Poverty Estimates for 2015 is the last full year for which data is available.