 On December 25, he became Acting Assistant Adjutant General of the Cavalry Corps of the Military Division of the Mississippi, with Major General James H. Wilson commanding.He was mustered out of service on July 1, 1865 and was subsequently brevetted major of United States Volunteers by President Andrew Johnson on March 13, 1866 for gallant and meritorious service during the American Civil War.After the war, Griffin returned to practice law in Detroit in his partnership with William A. Moore.