Inside a data center in Sterling. Some data center operators employ fewer than 10 people per facility. (Sarah L. Voisin/The Washington Post)

Ashburn is one of a handful of American boom towns for data centers, the anonymous warehouse-like homes for Internet servers.

In Ashburn and the rest of Loudoun County, there are 5.2 million square feet of data centers, the equivalent of 25 Wal-Mart super centers, within the county’s 521 square miles. That puts it in the very upper echelon of data center clusters in the country, rivaling Silicon Valley, the New York suburbs and the Dallas area.

As much as 70 percent of all Internet traffic flows through Loudoun County data centers each day, according to the county department of economic development, and the industry contributed some $60 million to the county tax rolls last year.

The boom came, however, without creating many jobs.

Only 1,300 people are employed by Loudoun’s data center empire. For example, one of the two titans of Northern Virginia’s data center empire, and the largest data center company in the world, is Digital Realty Trust. The company owns 24 million square feet of data centers worldwide, including 2.7 million square feet in Northern Virginia and 2 million in Ashburn alone.

But the company only employs about 50 people in Virginia, according to Dana Adams, vice president of portfolio management for Digital Realty Trust. Job titles include data engineers, sales associates and property managers to keep the servers comfortably humming 24 hours a day. But if Digital Realty Trust’s Virginia space was instead comprised by offices, it would likely be home to between 13,000 and 15,000 employees.

“We don’t necessarily employ as many people as in a large office tower, but we have quality jobs, and the counties like that,” Adams said.

Adams said that although the industry doesn’t create a ton of jobs, it still adds value to a community.

“I think it’s an interesting argument, but I think the reality is that over the last five years, the office market hasn’t really been there, and the data center market has been a great source of growth for these areas,” she said.

Adams is right about that. Beginning in 2010, when the traditional commercial real estate market was still suffering from the economic collapse, data centers took over Loudoun’s construction pipeline. Companies built 210,814 square feet of data center space that year, compared to 121,000 square feet of office space, according to the real estate services firm Jones Lang LaSalle. It was the first time builders built more data center space than office space in Loudoun.

Since then, the trend has continued. In the two years spanning 2011-2012, data centers were the only game in town: Loudoun added 790,583 square feet of data centers but no office space. In 2013, Loudoun added 428,086 square feet of data centers, more than four times what they added in office space.

This year, the county will add 12 times more data center than office space: 600,000 to 49,099, according to Jones Lang LaSalle’s prediction.

For the most part, the Loudoun County is okay with this. Data centers provide the county a commercial tax base without requiring much additional spending on schools, parks or fire and rescue services the way building new housing would. The unemployment rate has been running under 4 percent.

“It doesn’t have that big draw on services that other industries would have,” said Buddy Rizer, director of Loudoun County’s economic development department.

With only a handful of workers needed to maintain a mammoth data center, and many of them working unusual hours, the facilities create negligible traffic as well. The average commute in Loudoun County is already 33 minutes, and residents heading to Arlington or the District every day often sit in their cars twice that long.

Rizer proudly points out that Loudoun’s economy is less reliant on federal government jobs than most other parts of the region, making it less susceptible to government cutbacks. “Our economy is less dependent on the government than even Prince William is,” he said.

Still, it’s unusual for an economic development agency not to focus more closely on job creation, and Rizer said that may have to change as the county considers its strategy going forward. Loudoun is primed to receive its first three Metro stations on the second leg of the Silver Line, and it will not take advantage of them by surrounding them with warehouses bereft of human beings.

“As a business developer, data centers have been my life for the last bunch of years, so I’m really happy to see that growth and to see what we’ve achieved there,” Rizer said. “But as the director of economic development, I recognize that we have to continue to build a more balanced economy.”