Photo by Reid Kasprowicz

Half of the top 10 richest counties in the U.S. are in the D.C. region, according to a new ranking.

Four of them—Loudoun, Falls Church, Fairfax, and Howard—top the list, respectively. Arlington comes in at number 8.

Forbes’ 2017 list of the 10 Richest Counties in America is based on 2015 household income data from the Census Bureau. While their proximity to the District and federal government jobs are key to residents’ wealth, the report also names other companies that contribute to the six-figure median household incomes in the four Virginia suburbs and Howard County, Maryland.

Loudoun places first with an average household income of $125,900. The Department of Homeland Security is its biggest federal employer, and Verizon and Dulles Airport are among the 11,700 businesses that keep residents afloat.

Falls Church, which Forbes points out is actually a city with “county-level governance status” is the smallest place on the list with 12,000 people. But government jobs and private sector industries like healthcare contribute to their second-place status.

While Fairfax County comes in third today, it’s was the first U.S. county to reach a six-figure median household income, according to the report (Loudoun and Fairfax counties have also been ranked among the happiest counties in the country.)

Howard County residents made the list thanks to a John Hopkins University lab, which employs 5,000 people, in addition to the public school system and a Verizon Wireless regional headquarters.

And Arlington, which has also been ranked the best place for millennials and the third hippest place in the country, comes in eighth place. It’s home to the Pentagon and Department of Defense, which employs 24,000 residents.