On the date of the 14th of April 1864, while still encamped around Chattanooga, Tennessee, The 11th and 12th Corps were formally disbanded and their units consolidated into a new 20th Corps, under command of General Joseph "Fighting Joe" Hooker. The 55th Ohio was brigaded with former 11th Corps units (2oth Connecticut, 33rd Massachusetts, 136th New York, 73rd Ohio, 26th Wisconsin) in Colonel James Wood's 3rd Brigade of General Daniel Butterfield's 3rd Division. The 20th Corps was assigned to Major General George (Rock of Chickamauga) Thomas' Army of the Cumberland, one of three armies comprising General William T. Sherman's Great Army of the West. For its emblem, the corps took the badge of the old 12th Corps, a five pointed star (red for the 1st Division, white for the 2nd and blue for the 3rd Division).
Sources:
Trials and Triumphs: A Record of the Fifty-Fifth Ohio Volunteer Infantry by Hartwell Osborne, 1904, A.C. Clurg & Co., Chicago.