George, thanks for trying to help me. This William M. Johnson was not my direct line. He was a brother to my great grandfather, Joseph Abner Johnson. I just decided to try to find out what happened to my great grandfather's three brothers: Benjamin Gunnells Johnson, John H. Johnson, and William. William was the youngest, born in 1841, I believe, in Jefferson Co., Alabama. The family moved to Pontotoc Co., MS between 1845 and 1850. I figured, being born in 1841, he was the right age to fight in the Civil War, although I know he was still in Pontotoc in 1860, living with his mother, brother John H., all in the home of his sister, Susan. After 1860, I have no idea what happened to him. I don't know if he ever married - nothing. So, in answer to your question, I have no idea whatsoever IF he served, first of all, and if he did, I have no idea what unit.
Sue (Johnson) Howard