Major Clemens was one of four men guarding President Lincoln when he visited Richmond, Virginia, shortly after the fall of the Confederate capital.
In a letter written after Lincoln's assassination, Clemens wrote: "Here it is! Here it is! I can hardly realize the fact that the president is dead, as it has only been a few days since I had the pleasure of entering Richmond with him and passing as he did safely through the city without any protection whatever."
After the war, he was a bookkeeper for the Lehigh Valley Coal Company. He died June 2, 1894 in Pottsville, Pennsylvania and is buried in the Church of Brethern Cemetery in Germantown, Philadelphia County.