Before the outbreak of the Civil War, Alexandria County, the closest part of Virginia 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 city of Alexandria, at the far southeastern corner of the county. In 1861, the rest of the county largely consisted of scattered farms, the occasional house, fields for grazing livestock, and Arlington House, owned by Mary Custis, wife of Robert E. Lee.