I have been unable to ID your William Thompson in the Confederate army under either the given name William or Alexander

1860 United States Federal Census about Sophia Thompson
Name: Sophia Thompson
Age in 1860: 36
Birth Year: abt 1824
Birthplace: Georgia
Home in 1860: Townships 14 and 15, St Clair, Alabama
Gender: Female
Post Office: Ashville
Value of real estate: View Image
Household Members:
Name Age
Alx Thompson 40 Farmer
Sophia Thompson 36
Drucilla Thompson 16
Albert Thompson 14
Indianna Thompson 10
Daniel Thompson 4
William Thompson 2
John Thompson 10/12

........

Civil War service men from St. Clair County served in various regiments. Men often joined a company (within a regiment) that originated in their county. Listed below are companies or regiments that were formed from men of St. Clair County.

- 10th Regiment, Alabama Infantry, Company A "Ashville Guards"
- 10th Regiment, Alabama Infantry, Company F "Coosa Valley Guards"
- 25th Regiment, Alabama Infantry, Company D and H
- 30th Regiment, Alabama Infantry, Company H
- 51st Regiment, Alabama Partisan Rangers, Company E
- 58th Regiment, Alabama Infantry, Company A, C, G and I