The following information is courtesy of GMU's webpage.

George Mason University opened the doors of its Prince William Campus on August 25, 1997. Along with existing campuses in Fairfax and Arlington counties, it became the university’s third campus in Northern Virginia and welcomed approximately 800 students to a single multipurpose building. Today, the 124-acre campus serves more than 2,000 students in four innovative facilities specially designed for classrooms, laboratories, libraries, recreation, and other uses.

The Prince William Campus is located approximately 30 miles west of the nation’s capital in the Innovation@Prince William research and development business park. Along with its neighbors -- American Type Culture Collection, Lockheed Martin Federal Systems, Comcast Communications, SAIC, and others -- the campus is a major contributor to a competitive environment for pioneering academic, research, and business activities.

Along with administrative, teaching, and research spaces, the Prince William campus is home to such facilities as the 300-seat Verizon Auditorium, the Freedom Aquatic and Fitness Center , the Mason Enterprise Center, the Community Performing Arts Center, and a Regional Biocontainment Laboratory.

DIRECTIONS TO PRINCE WILLIAM CAMPUS (10900 University Blvd., Manassas, VA 20110) from East or West along I-66 and points North:
From I-495, take exit 49 to 66 West. From I-66, take Exit 44, Route 234 South. Travel approximately 4 miles, and turn left at the fourth signal, University Blvd. The Prince William Campus will be on your left. Turn left at Freedom Center Boulevard to enter campus.
*Note: All westbound lanes of I-66 inside the Beltway are restricted to HOV-2 from 4:00 pm to 6:30 pm.

DIRECTIONS TO PRINCE WILLIAM CAMPUS (10900 University Blvd., Manassas, VA 20110) from I-95 & Eastern Prince William County:
From I-95, take Exit 152 (Route 234 - North, Dumfries Road). Travel approximately 19 miles on Route 234 North. Stay on Route 234 as it becomes Prince William Parkway. One half mile past the Route 28-Manassas interchange, turn right on University Blvd. The Prince William Campus is on the left. Turn left at Freedom Center Boulevard to enter campus.

Sources:
Prince William Information Page