 Fairfax County is the most populous locality in Virginia , with over one million residents , although that does not include its county seat Fairfax , which is one of the independent cities . Fairfax County has a major urban business and shopping center in Tysons Corner , Virginia 's largest office market . Neighboring Loudoun County , with the county seat at Leesburg , is both the fastest @-@ growing county in Virginia and has the highest median household income ( $ 114 @,@ 204 ) in the country as of 2010 . Arlington County , the smallest self @-@ governing county in the United States by land area , is an urban community organized as a county . The Roanoke area , with an estimated population of 300 @,@ 399 , is the largest Metropolitan Statistical Area in western Virginia . 
