On September 2nd, 1864 the Union 20th Corps led the Union forces under General William T. Sherman into the besieged city of Atlanta, Georgia. The 55th Ohio sent in a detachment this day, with the remainder of the regiment following on September 4th. Since leaving Chattanooga, the 55th Ohio had lost about 200 total casualties (40 killed / mortally wounded, 160+ wounded, missing or captured). This was about half of the manpower the regiment left Chattanooga with! The 55th Ohio was posted in the city's defenses on the southeast side, and remained there for the remainder of the occupation, except for occasional excursions into the countryside to forage (as the rebs would occasionally harass the single rail line into the city). The whole 20th Corps garrisoned the city while General Sherman took the remainder of his forces and attempted to chase down John B. Hood's rebels to the northwest. While in this duty, the 55th Ohio received about 196 new recruits to swell its depleted ranks, of which 181 were either draftees or substitutes. 74 men, who did not re-enlist with the rest of the regiment, were also discharged. Along with the other various fluctuations in it's ranks such as death from disease, transfers, resignations and prisoners taken (8 men were captured apparently during a foraging expedition), the regiment had about a "net gain" of 100 men, making the ranks about 300 men total. On September 24th 1864, Lt. Col. Philo Buckingham (20th Connecticut Infantry) assumed command of the 3rd Brigade, 3rd Division of the 20th Corps, in place of Col. James Wood (reason unknown).
Sources Trials and Triumphs by Hartwell Osborne, 1904
All Brave and True by Dan Munson, 1986