Samuel P. Duncan served as a 2nd Corporal with Company D, 4th Regiment of Kentucky Volunteers during the Mexican American War. He joined the Company at Bedford, Trimble County, Kentucky in September of 1847 and was mustered into service on October 2, 1847. He mustered out with his regiment at Louisville, Kentucky on July 25, 1848. He would later serve as a captain in Company E of the 4th Kentucky Cavalry (Confederate) during the Civil War.
From the description of Samuel Pryor Duncan letter, 1861-1864 (Murray State University). WorldCat record id: 618553308