Good find! I dug a little further based on the obituary mentioning that he was from Mattson. That unincorporated community is located in Coahoma County. NPS Soldiers and Sailors shows a J. Langston in the 18th Mississippi Cavalry, but I do not find a CMSR for that man. That regiment was partially raised in Coahoma County, so he remains a possibility. Also - checking the Mississippi Confederate Grave Registry site, I find that they show him in Co. H, 11th Mississippi Cavalry. Looks like more research is needed to positively identify the unit.