The Fairfax County Economic Development Authority just announced that Fortune Magazine has released its annual list of the 500 companies in the country with the largest revenue.  A total of  eight (up from seven in 2009) Fairfax County-based companies grace the list. Tysons Corner-based mortgage behemoth Freddie Mac comes in at 54, and defense-industry giant Merrifield-based General Dynamics is 69. Other Fairfax County firms on the list are Merrifield-based CSC (138), Tysons Corner-based Capital One Financial (144), Tysons Corner-based Science Applications International Corporation (SAIC) (215), Reston-based NII Holdings (468), Reston-based SLM (Sallie Mae) (354), and Tysons Corner-based Gannett (370). Fortunately, you can get the rest of the story from the Washington Business Journal’s Jeff Clabaugh.