In 1861, at the start of the American Civil War, Hotaling helped raise a company of Union cavalrymen that was recognized by the Army as Co. A, 2nd Illinois Cavalry Regiment. His brother Nick, who had also moved to Ogle County from New York, enlisted and served along with him. Three of Hotaling's other brothers served in Eastern Regiments. Hotaling, newly commissioned as a captain, was one of the commanding officers of Company A. He would also command company B of the same regiment at various times.