Together, they inject $10 billion from paychecks and contracts into the region's economy every year - a figure that helps explain the rest of the Fort Meade cluster, which fans out about 10 miles in every direction.
Just beyond the NSA perimeter, the companies that thrive off the agency and other nearby intelligence organizations begin. In some parts of the cluster, they occupy entire neighborhoods. In others, they make up mile-long business parks connected to the NSA campus by a private roadway guarded by forbidding yellow "Warning" signs.
The largest of these is the National Business Park - 285 tucked-away acres of wide, angular glass towers that go on for blocks. The occupants of these buildings are contractors, and in their more publicly known locations, they purposely understate their presence. But in the National Business Park, a place where only other contractors would have reason to go, their office signs are huge, glowing at night in bright red, yellow and blue: Booz Allen Hamilton, L-3 Communications, CSC, Northrop Grumman, General Dynamics, SAIC.
More than 250 companies - 13 percent of all the firms in Top Secret America - have a presence in the Fort Meade cluster. Some have multiple offices, such as Northrop Grumman, which has 19, and SAIC, which has 11. In all, there are 681 locations in the Fort Meade cluster where businesses conduct top-secret work.
Inside the locations are employees who must submit to strict, intrusive rules. They take lie-detector tests routinely, sign nondisclosure forms and file lengthy reports whenever they travel overseas. They are coached on how to deal with nosy neighbors and curious friends. Some are trained to assume false identities.
If they drink too much, borrow too much money or socialize with citizens from certain countries, they can lose their security clearances, and a clearance is the passport to a job for life at the NSA and its sister intelligence organizations.
Launch Photo Gallery »
Chances are they excel at math: To do what it does, the NSA relies on the largest number of mathematicians in the world. It needs linguists and technology experts, as well as cryptologists, known as "crippies." Many know themselves as ISTJ, which stands for "Introverted with Sensing, Thinking and Judging," a basket of personality traits identified on the Myers-Briggs personality test and prevalent in the Fort Meade cluster.
The old joke: "How can you tell the extrovert at NSA? He's the one looking at someone else's shoes."
"These are some of the most brilliant people in the world," said Ken Ulman, executive of Howard County, one of six counties in NSA's geographic sphere of influence. "They demand good schools and a high quality of life."
The schools, indeed, are among the best, and some are adopting a curriculum this fall that will teach students as young as 10 what kind of lifestyle it takes to get a security clearance and what kind of behavior would disqualify them.
Outside one school is the jarring sight of yellow school buses lined up across from a building where personnel from the "Five Eye" allies - the United States, Britain, Canada, Australia and New Zealand - share top-secret information about the entire world.
The buses deliver children to neighborhoods that are among the wealthiest in the country; affluence is another attribute of Top Secret America. Six of the 10 richest counties in the United States, according to Census Bureau data, are in these clusters.