According to the American Community Survey's new five-year estimates (2012-2016), the five richest counties in the country are: Loudoun County, Va., where the median household income was $125,672; Falls Church City, Va., where it was $115,244; Fairfax County, Va., where it was $114,329; Howard County, Md., where it was $113,800; and Arlington County, Va., where it was $108,706.
An additional four Washington-area counties made it into the Top 20: No. 9 Fairfax City, Va. ($104,065); No. 14 Montgomery County, Md. ($100,352); No. 17 Prince William County, Va. ($98,546); and No, 20 Stafford County, Va. ($97,606).
That gave the Washington, D.C. area a total of 9 out of the 20 richest counties in the United States.
Five of the Top 20 richest counties were in northern New Jersey or New York: No. 6 Hunterdon County, N.J. ($108,177); No. 10 Morris County, N.J. ($102,798); No. 11 Somerset County, N.J. ($102,405); No. 12 Nassau County, N.Y. ($102,044); and No. 19 Putnam County, N.Y. ($97,606).
Another three of the Top 20 richest counties were in California in the San Francisco Bay Area: No. 13 Santa Clara County ($101,173); No. 15 Marin County ($100,310); and No. 17 San Mateo County ($98,546).
The Census Bureau treats independents cities—such as Falls Church City, Va., and Fairfax City, Va.—as counties, which is why they are included on the list.
The nationwide median household income in 2012-2016, according to the Census Bureau, was $55,322. That means that the income in the nation's four richest counties—Loudoun, Falls Church City, Fairfax County, and Howard County—were all more than double the national median.
The median household income in Arlington County, the nation’s fifth richest county, which sits directly across the Potomac River from Washington, D.C., was 96.5 percent greater than the national median.