 Before the outbreak of the Civil War, Alexandria County (renamed Arlington County in 1920), the closest Virginia county to Washington, D.C., was a predominantly rural area.Originally part of the District of Columbia, the land now comprising the county was retroceded to Virginia in a July 9, 1846 act of Congress that took effect in 1847.Most of the county is hilly, and at the time, most of the county's population was concentrated in the town of Alexandria at the southeastern corner of the county.