Forbes rounds up the richest counties in the US, with the DC suburbs in northern Virginia again dominating. The top five: 
 -  Loudoun County, Virginia: $115,574 median household income
  -  Falls Church City, Virginia: $114,409
  -  Fairfax County, Virginia: $105,416
  -  Los Alamos County, New Mexico: $103,643
  -  Howard County, Maryland: $103,273
  
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full list, which includes one more DC suburb cracking the top 10, along with one more from the West.