I will add a few observations. I agree with Alan that there is little hard data of just how many civilains became "casualties" during the March to the Sea. It is largely a definitional probelm. If youy restirct it to how many were shot by Federal troops, I suspect that the number would be small. If you include those who died of malnutrition, exposre, etc., the number would be very much larger, but how many it would be would be, I suspect, rank speculation. There were no death certificates at that time, few if any public hospitals along or adjacent to the lien of march, so records simply don't exist. I suspect any evidence will be anecdotal.
A couple of observations. When Sherman prepared for the march, he emptied Atlanta of its civilian population (which was greatly swollen in size due to the existence of wartime industry and transportation sector manpower needs, and due to refugees who had come to the city, principally from North Georgia. If I udnerstand it correctly, the civilians who did not elave voluntarily were put on trains, and taken to the end of the tract at Jonesboro, and literally dumped into the woods. This was in mid-November, 1864, and there were no facilities to care for the civilians, free and slave both. Just how many of these unfortunates died of exposre, pneumonia, or other related ailmenst is not known,. but it could not ahve been anything but a substantial figure. Certtainly the destruction of warehouses, factories, and transportation facilities were legitimate miltary objectives, but the fire destroyed a large number of the houses in the city. When the inhabitants returned, in amny cases thery had no shelter from the north Georgia winter.
I want someone more versed than I to correct me if I am in error, but I seem to recall a terrible incident at the crossing of the Ogeechee River, near the end of the march. As the Federals moved southeast, a large number of slaves left their plantations and followed in the wake of the Federal army. I believe the number was well into the thousands. They came ot be a burden on the ability fo the Union commissary to feed them. When the Federal rear guard crossed the roiver, ahead of the throng of slaves who were follwoing the army, the Federals set fire to the bidge. A large number jumped into the river to try to swim to the southeastern bank, and were drowned. Apparently no effort was made by the rear guard to save any of them, but it relieved Sherman of the "problem."
Sherman was in many cases the Nineteenth Centry Teflon man. Even by the standards of the day, acts such as the wanton burning of a major city, churches, etc., or the destruction of purely civilian targerts, would have been considered unacceptable, but somehow Sherman always managed to defelct any blame upon his sobordinates, bummers, Wheeler (though Wheeler's men were little better than the bummers in many cases), or someone else.
The destruction in Georgia, bad as it was, was unmatched by the destruciton in South Carolina; Sherman said, before he started his march into South Carolina at the beginning of February, 1865, that he "trembled" for the fate of South Carolina. The issue of "Who burned Columbia?" is debated yet, but there is no question that eveyr other town which Federal troops visited on the march weas put to the torch. Barnwell (but he spared the Episcopal Church, because the Federal officers used it for a stable; the hoof prints are still visible in the floor), Blackville, Brahchville, Orangeburg, Lexington, and Winnsboro were all ptu to the torch. Mary Boykin Chesnut, returning to her home in Camden in late April, described her trip from Chester (which Sherman just by-passed) toward the Wateree River, across the line of march, and she stated that there was not one house left standing in a forty mile swath --all burned.