I am not certain that he was born in Alabama. I'll have to look at the 1870 census record again, and I know that that is not 100% reliable. I do not know what the S stands for.
The letter was addressed to Mr. W.A. (Bill) Hopkins in Franklin County, Alabama. The letter was purchased by my cousin from a Mr. Winchester after he saw a printed copy in a genealogical magazine he saw in Florence, AL. My cousin mentioned that our John S. Goodwin is the only J.S. Goodwin in Franklin Co. during the 1870s time period, therefore the J.S. Goodwin listed on the Civil War Roll of Company E, Fourth Alabama Cavalry is likely the same person. That's the extent of anything that we have been able to find.
Thank you for your interest.