On May 3, 1808, Taylor joined the U.S. Army, receiving a commission as a first lieutenant of the Seventh Infantry Regiment from his cousin James Madison. He was ordered west into Indiana Territory, and was promoted to captain in November 1810. He assumed command of Fort Knox when the commandant fled, and maintained command until 1814.
- General Zachary Taylor
During the War of 1812, Taylor successfully defended Fort Harrison in Indiana Territory, from an attack by Indians under the command of Shawnee chief Tecumseh.
- Likely painting of Tecumseh
As a result, Taylor was promoted to the temporary rank of major, and led the 7th Infantry in a campaign ending in the Battle of Wild Cat Creek. Taylor was also commander of the short-lived Fort Johnson (1814), the last toehold of the U.S. Army in the upper Mississippi River Valley until it was abandoned and Taylor's troops retreated to Fort Cap au Gris.
Reduced to the rank of captain when the war ended in 1814, he resigned from the army, but reentered it after he was commissioned again as a major a year later. In 1819, he was promoted to the rank of lieutenant colonel and was promoted to full colonel in 1832
- Fort Johnson