During the Civil War, more soldiers passed through Poolesville than any other Montgomery County town. Union forces occupied the village through most of the war to protect the strategic road network and lines of communication and supplies. Confederate cavalry occasionally raided the Federal cavalry units stationed there, and Company B of local resident Confederate Col. Elijah Veirs White's 35th White's Ferry Cavalry Battalion included Poolesville natives. When the Army of the Potomac crossed the Potomac River at Edwards Ferry on June 24-25, 1863, and marched to Frederick and then to Gettysburg, Poolesville became temporary Union headquarters. Four infantry corps, the cavalry corps, and the Artillery Reserve passed through town June 25-27, 1863, and Gen. Winfield S. Hancock commandeered the home of elderly Jessie Veirs, Col. White's cousin. Telegraph records indicate Gen. Joseph Hooker, commander of the Army of the Potomac, arrived on the evening of June 26; at 9:00 a.m. on June 27, he left for Harpers Ferry, where he would resign his command in a letter to President Abraham Lincoln. Nearby at Seneca Mills, on June 10, 1863, Confederate Col. John S. Mosby's 43rd Virginia Battalion of partisan rangers crossed into Maryland to reconnoiter for Gen. J.E.B. Stuart. The next day, separated from Stuart by the Union army, Mosby attacked a 6th Michigan Cavalry outpost at Seneca, and the Federal troopers retreated to Poolesville to regroup for an assault that never came. Mosby lost two men, Lt. George H. Whitescarver and Capt. William G.D. Brawner of Company H, 15th Virginia Cavalry, whose men had joined the raid to share in spoils that rangers were allowed to keep.