Fort McHenry was constructed between 1799 and 1802. It was in the shape of a five-pointed star, which was a popular design during the period. Each point of the star was visible from the point on either side and every area of land surrounding the fort could be covered with as few as five men.

The walls of Fort McHenry and the buildings within were constructed of brick. There were four barracks to house the garrison consisting of the Commanding Officer's Quarters, Junior Officers' Quarters and two buildings for the enlisted men. A guardhouse stood next to the Commanding Officer's Quarters. Here, soldiers of the Fort McHenry Guard lived and worked, and sometimes unruly soldiers were confined in the guardrooms. The Powder Magazine, where the gunpowder was stored, stood between the Commanding Officer's Quarters and the Junior Officers' Quarters. The magazine was of solid enough construction to protect the gunpowder from sparks, fire and explosion.

During the 1830's, major improvements were made to the fort. Second stories were added to the barracks and two new guardhouses were built on each side of the Sally Port to replace the two earlier ones.