Just your average run-of-the-mill mansion in Loudoun County, where the median household income last year was $119,134, the highest in America. (Heather Elias - Century 21 Redwood)

The Post’s Carol Morello and Ted Mellnik note that the Washington area, flush with federal contractors and high-tech companies, now has seven of the 10 most affluent counties in the country. While Loudoun’s median income dropped by $400, that was within the margin of error of the survey. Arlington’s median income, which was previously fifth highest, rose by almost $6,000, and Fairfax’s rose by nearly $3,000, making the three NoVa counties the only ones in the U.S. with median incomes over $100,000.

Prince William (about $2,500) and Alexandria (about $5,000) also saw significant jumps in income. Fauquier and Stafford counties, on the border of the State of NoVa, were ranked eighth and 13th respectively, and Montgomery County, Md., was 10th.

Here are NoVa’s stats and national ranking for 2011:

Alexandria (26th): $82,748; median household income up $4,955

Arlington (3rd): $100,735; up $5,749

Fairfax (2nd): $105,797; up $2,787

Loudoun (1st): $119,134; down $406

Prince William (7th): $95,146; up $2,491

Here’s the list of the Top 100 wealthiest counties in America.

Though this topic has been widely discussed before, you are certainly welcome to post your theories on why NoVa tops this list every year in the comments.