I found some references to Nathan Sexton in a case filled for claims against the Choctaw & Chickasaw Nations by J.G. Heald after the war. It appears Sexton was district attorney and clerk prior to the war.

https://books.google.com/books?id=TVhHAQAAIAAJ&pg=RA2-PA15&lpg=RA2-PA15&dq=nathan+sexton+choctaw&source=bl&ots=sgSgLrYWla&sig=K2Zp_IOTzAi_KT_3cf0-Ka-qe8Q&hl=en&sa=X&ved=0ahUKEwiXmbbM4unXAhVE94MKHTjIANsQ6AEIRTAF#v=onepage&q=sexton%20&f=false