The Library of Congress online archive has this photographic treasure:
And here’s a transcription of the photo’s description printed on the back of the image:
Colonel, the subject of this sketch, was about six years old at the breaking out of the Rebellion, and was owned by Lieut. N.J. Hall, of the 5th U.S. Artillery whose home was at Monroe, Michigan. Lieut. Hall purchased the “Colonel” at Charleston, S.C., and as he (Hall) was one of the officers under Major Anderson in Ft. Sumter, when the first shot was fired at that heroic garrison, “Old Colonel” must have heard the first gun that was fired at our National Flag. Lieut. Hall was soon after assigned to duty on Gen. George B. McClellan’s staff and rode “Colonel whilst with that general from Ball’s Bluff to Harrisons Landing. In July 1862, Hall was promoted to Col. of the 7th Michigan Infantry and was in command of the Regiment, or a Brigade, up to and including the battle of Gettysburg. “Colonel” was wounded in the left shoulder at the battle of Antietam, but recovered in time to participate in the battle of Fredericksburg, and was in active service until the 2d of July, 1863, when he was again wounded at Gettysburg in the left hip. Col. Hall was about this time ordered to Grand Rapids, Michigan, and “Old Colonel” was left in charge of the Quartermaster of the 7th (W.W. Wade of Jonesville). Wade brought the horse to Michigan in January 1864, and had charge of him until the close of the war. In the meantime Col. Hall had been ordered to Brooklyn, N.Y. Lieut. Wade kept the horse until 1866 and wrote to Hall asking what he should do with him. Hall instructed Wade to sell him, with the understanding that he (Hall) could buy him back at any time for the purchase price. Col. Hall died in 1878 and as nothing had been heard from his family or friends, the Hillsdale County Soldiers and Sailors Reunion Association bought “Colonel” in 1879 and have cared for him since.
List of Battles which “Colonel” was in:
Fort Sumter, Balls Bluff, Siege of Yorktown, Williamsburg, Fair Oaks, Mechanicsville, Gaines Mill, Savage Station, White Oak Swamp, Glendale, Malvern Hill, Bull Run Second, South Mountain, Antietam, Fredericksburg, Chancellorsville, Hay Market, Gettysburg.
Library of Congress: https://www.loc.gov/item/2015650837/