The most aggressive players at present seem to be Raytheon, Science Applications International, General Dynamics and Lockheed Martin, but other players like BAE Systems and Boeing are rapidly bulking up.

FORBES: Cyberwarfare May Be A Bust For Many Defense Contractors

The county is dotted with military bases and intelligence sites such as CIA headquarters, and most of its biggest private-sector employers are defense contractors like General Dynamics, Northrop Grumman and Science Applications International.

FORBES: Defense-Heavy Fairfax County, Va., Could Decide Presidential Race