1st Battle of Bull Run, July 16-22, 1861
All ten companies, A to K, were in service by June 8, 1861, so I would hazzard a guess that all ten were there at the time, with the possible exception of Co I which was the last to enlist.
2nd Regiment, Virginia Cavalry
2nd Cavalry Regiment completed its organization at Lynchburg, Virginia, in May, 1861. Its companies were recruited in the counties of Bedford, Campbell, Botetourt, Amherst, Franklin, Appomattox, and Albemarle. Until the end of October the unit was called the 30th Regiment Virginia Volunteers. During the war it was brigaded under Generals B.H. Robertson, F. Lee, Wickham, and Munford. The 2nd Cavalry saw action at First Manassas, in Jackson's Valley Campaign, and at Groveton Heights, Sharpsburg, Fredericksburg, Kelly's Ford, Chancellorsville, Brandy Station, Aldie, Upperville, Gettysburg, and Shepherdstown. After the Bristoe and Mine Run campaigns, it was involved at The Wilderness, Todd's Tavern, Spotsylvania, Haw's Shop, and Cold Harbor. It fought in the Shenandoah Valley with Early and later in numerous conflicts around Petersburg and Appomattox. The regiment contained 676 men in July, 1861, lost twenty-eight percent of the 163 engaged at Groveton Heights, and of the 385 at Gettysburg about four percent were disabled. At Appomattox it cut through the Federal lines and disbanded at Lynchburg on April 10, 1865. However, 19 men were included in the surrender. The field officers were Colonels Thomas T. Munford and Richard C.W. Radford, Lieutenant Colonels Cary Breckinridge and James W. Watts, and Major William F. Graves.
Co A - Clay Dragoons, Bedford County; Enrolled at Liberty [now Bedford] May 11, 1861 & mustered in same date at Lynchburg
Co B - Wise Troop, Lynchburg, Campbell County; organized November 1859; enrolled & mustered in at Lynchburg, May 13, 1861
Co C - Botetourt Dragoons, Botetourt County; organized at Fincastle in January, 1860; enrolled there May 17, 1861; mustered at Lynchburg, May 20, 1861
Co D - Franklin Rangers, Franklin County; enrolled at Franklin, May 20, 1861; mustered at Lynchburg, May 22, 1861
Co E - Amherst Mounted Rangers, Amherst County; enrolled at Amherst Court House, May 12, 1861; mustered at Lynchburg, May 29, 1861
Co F - Bedford Southside Dragoons, Bedford County; enrolled at Davis' Mills on May 28, 1861; mustered in at Lynchburg, May 31, 1861
Co G - Radford Rangers, Bedford County; enrolled at Forest Depot May 28, 1861; mustered at Lynchburg May 29, 1861
Co H - Appomattox Rangers, Appomattox County; enrolled at Appomattox Court House May 24, 1861; mustered at Lynchburg June 3, 1861
Co I - Campbell Rangers, Campbell County; enlisted June 8, 1861
Co K - Albemarle Light Horse, Albemarle County; Organized January, 1861; enlisted May 11, 1861