Try these cards on for size

http://www.sos.mo.gov/archives/soldiers/details.asp?id=S417607&conflict=Civil%20War&txtName=Thurmond&selConflict=Civil%20War&txtUnit=&rbBranch=all#

http://www.sos.mo.gov/TIF2PDFConsumer/DispPDF.aspx?fTiff=/archives/AdjutantGeneral/Civil_War/ServiceCards/s739/3248.tif&Fln=S417606.pdf

http://www.sos.mo.gov/TIF2PDFConsumer/DispPDF.aspx?fTiff=/archives/AdjutantGeneral/Civil_War/ServiceCards/s739/3251.tif&Fln=S417609.pdf

All three are your fellow and confirms he was from Pike County.
Thanks for sharing the letter and it appears he was in the thick of the war for a Missourian.

John R