John A. Dietz (November 24, 1870 – October 11, 1939) was an American sports shooter who competed at the 1908 Summer Olympics and the 1912 Summer Olympics. He won two gold medals as part of the American pistol team.In 1908 he also competed in the individual pistol event and finished ninth. In 1912 he finished fourth in the 30 metre military pistol team event. He also competed in the 30 metre rapid fire pistol event finishing fourth and in the 50 metre pistol finishing again ninth.