Grave Marker Question - What does Corp. Co. C, 14th T-INF mean and what war might the person have fought in?

He was a militiaman who probably served in the Spanish American War (1898-1899) which was the last war Volunteer Militia was used in as he was a Corporal in Company C of the 14th Tennessee Infantry Regiment. The First World War for the United States start the year following his death and he was far too young to for the Civil or Indian Wars.

The 14th Infantry was bouncing around in the Pacific Theater after the Civil War. It was at Presido San Francisco during the Civil War and is now part of the 25th ID Schofield Barracks HI.

This guy was born 13 years after the Civil War and would have been buried in the Philippines if he had died in combat. That is where the 14th was in 1916.

Edit: There was a 14th in the Confederate Army. Since it was disbanded 13 years before his birth the math just does not work.

I would say your assumption is off by one war. I would say he was a corporal for the company C of the Tennessee Infantry and that he fought in the Spainish-American war of 1898. The regular army as we would know it today didn't exist yet they were still know by there militia names like 6th Vermont or 23rd Massachusetts. The US didn't enter WW1 until 1917.