Arlington County is a county in Virginia. It has so many buildings that it looks like a city. It is one of the smallest counties in the United States by area. It is across the Potomac River from Washington, D.C., and parts of it were once part of Washington. 210,000 people live there. It is where many U.S. government offices are, such as The Pentagon. It is also the location of Arlington National Cemetery, which was built at the former plantation of Robert E. Lee, and the Ronald Reagan National Airport. ANC is where John F. Kennedy and many American soldiers are buried. Several battles of the American Civil War were fought in and around Arlington.