For four days in March 1862, the Pennsylvania Reserve Corps camped at Hunter's Mill after leaving Camp Pierpont at Langley on March 10 under orders of Union Gen. George B. McClellan, commander of the Army of the Potomac, who had heard that Gen. Joseph E. Johnston's Confederate army had evacuated northern Virginia for Richmond. The corps prepared for the Peninsula Campaign and remained there until March 14, when it broke camp and headed to Alexandria. Gen. George A. McCall commanded the corps, which consisted of three brigades under Gens. George G. Meade, Edward O.C. Ord, and John F. Reynolds. Civil War correspondent George A. Townsend wrote of the rainy evening departure on March 14 that although 15,000 men made up the corps, each brigade would have seemed as numerous to a novice, while country people gathered in fright at cottage doors and farm dogs bayed at the unusual scene. Hunter's Mill, a grist mill and sawmill named for George W. Hunter, Sr., who acquired it in 1831, was described by Townsend as a storm-beaten structure that looked like a great barn. The Hunter's Mill area changed hands several times during the war. The Alexandria, Loudoun, and Hampshire Railroad was completed past this point in January 1860, allowing easy access between Alexandria and Leesburg. Abundant water, forage, and farm fields could sustain thousands of men and horses, but at an immense cost to the community, which took decades to recover.