My great-great-grandfather was commissioned and served as an Assistant Surgeon in the 15th USCT (Infantry) after having served as a Private in the 125th Illinois Infantry.
In a letter home to his wife in July 1864, he marks it as coming from Camp Donaldson, Nashville, TN. He also mentions his work in Cumberland Hospital. Being a CW novice, I thought he might actually have been at Fort Donelson but that seems too far away for him to call Nashville. I also have evidence that he traveled to/from a detachment of the 15th in Springfield.
I would like to pinpoint the location of this Camp (and Hospital).