10 of the Nations 20 Richest Counties Surround Washington DC

1. Fairfax County, Va.  Median income: $100,318

2. Loudoun County, Va. Median income: $99,371

3. Howard County, Md.   Median income: $94,260

4. Hunterdon Country, N.J.  Median income: $93,297

5. Douglas County, Colo.  Median income: $92,125

6. Somerset County, N.J.  Median income: $91,688

7. Morris County, N.J.  Median income: $89,587

8. Montgomery County, Md.  Median income: $87,624

9. Arlington County, Va.  Median income: $87,350

10. Nassau County, N.Y.  Median income: $85,994

11. Stafford County, Va.  Median income: $85,014

12. Calvert County, Md.   Median income: $84,891

13. Forsyth County, Ga.  Median income: $83,682

14. Putnam County, N.Y.  Median income: $81,907

15. Marin County, Calif.  Median income: $81,761

16. Williamson County, Tenn.  Median income: $81,449

17. Santa Clara County, Calif.  Median income: $80,838

18. Prince William County, Va.  Median income: $80,783

19. Alexandria City, Va.  Median income: $80,449

20. Charles County, Md.   Median income: $80,179

source Forbes.com