This is the No. 1 highest-earning region in the US, and it isn't in New York or California

Two women sit outside the Lincoln Memorial in Washington, D.C.

The five counties with the highest median household income in the U.S. are all clustered together right outside of Washington, D.C., in Maryland and Virginia, an area locals refer to as the DMV.

The group consists of Loudoun County, Fairfax County, Howard County, Fall's Church and Arlington County, according to recent data from the U.S. Census Bureau's 2013-2017 American Community Survey five-year estimates. The comprehensive survey includes a range of data for all 3,142 counties, nationwide, including statistics on economic, housing and social trends.

Residents of Loudoun County, the highest-earning area on the list, have a median household income of $129,588. The second-highest earning county, Fairfax, has a median household income of $117,515. Even No. 5 on the list, Arlington County, boasts a median household income of $112,138.

Here's a closer look at each place.

1. Loudoun County, Virginia

Median household income: $129,588
Number of households: 121,299

2. Fairfax County, Virginia

Median household income: $117,515
Number of households: 393,380

3. Howard County, Maryland

Median household income: $115,576
Number of households: 111,337

4. Falls Church (city), Virginia

Median household income: $114,795
Number of households: 5,308

5. Arlington County, Virginia

Median household income: $112,138
Number of households: 102,310

These locations rank higher on the Census Bureau's list than notoriously pricey and high-income metro areas such as San Francisco and New York City. But the DMV isn't home to Wall Street titans or Silicon Valley billionaires.

Instead, because of their proximity to the nation's capital, these counties attract high-paying jobs in fields such as law and policy. And a lot of these professionals marry each other, which consolidates the wealth.

"You have a two-lawyer household, which is a pretty common feature in this region, and the median household income gets pulled up pretty quickly," says Mark Trekson, a research associate at the Metropolitan Housing and Communities Policy Center.

One major reason the region is the highest-earning place in the U.S. is because the industries in the area, including government and defense jobs, are relatively stable and tend to be lucrative, Trekson says: "Broadly speaking, you have a lot of pretty highly-paid professionals in the region and historically it's been a white-collar town."

Unlike cities such as Detroit, which grew in conjunction with a boom in automotive manufacturing, D.C. isn't home to much heavy industry, Trekson points out. So while the population of the DMV has expanded over the past 50 years, it hasn't been affected by some of the downturns in manufacturing that hurt other places.

Basically, "the composition of the jobs in this region are pulling up the income and there's not a lot of massively declining job categories in the region that are pulling down incomes as well," Trekson says.

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Plus, these counties are home to a population with relatively homogenous incomes. There's more variety in what people earn in the San Francisco and New York City areas.

"If you're looking at the Bay Area, there's Oakland, for instance, which is a massive manufacturing and shipping hub," Trekson says. "If you have slightly lower levels of income in some of those areas, it means that the average is lower and the median is lower."

Still, there isn't a huge difference between the household incomes in the No. 2 through No. 4 spots and similarly high-ranking counties in California and New York, Trekson says. No. 11, Santa Clara County, the highest-earning county in California, boasts a median household income of $106,761. No. 13, Nassau County, New York, has a median household income of $105,744.

What pushes D.C. and its surrounding areas just ahead of the competition is the fact that it's home to a concentrated number of white-collar, high-paying jobs. "In a way, every city and metro area has those kinds of people, but there's just a lot of them in D.C.," Trekson says.

Although the region is far more diverse than just "a bunch of lawyers and consultants," he continues, "there's some level of truth to that, and that gets reflected on the ground."

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