Alexandria is an independent city, located in Northern Virginia surrounded by major counties like Fairfax County and Arlington County, and is bordered by the east by Potomac River. It is only 7 miles south of Washington D.C. so the city is mostly populated by employees in the federal government or U.S Military; its largest employer is the Department of Defense. Other federal agencies based in the city are the National Credit Union, U.S. Patent & Trademark Office, National Science Foundation, etc.