John S. Kountz (March 25, 1846 – June 14, 1909) was a soldier in the United States Army during the American Civil War.

At the Battle of Missionary Ridge, when the drum corps was ordered to the rear, he threw away his drum, seized a musket, and was severely wounded in the first assault, being left in the field under the enemy's guns until he was rescued by his company.

This episode was the subject of a poem by Kate B. Sherwood, entitled "The Drummer-Boy of Mission Ridge", which attained a wide reputation.

He was connected with the Grand Army of the Republic since its organization in 1866, and was elected 13th Commander-in-Chief on July 25, 1884.

In the presidential contest that occurred during his official term, he issued an order to bar politics from this organization.