Fort Duncan was established in 1849 as a U.S. Army post on the Rio Grande at Eagle Pass, functioning as a border-defense garrison that protected the western Texas frontier, guarded the river crossing and nearby trade route into Mexico, and supported campaigns against raiding parties. Troops based there carried out routine patrol, escort, and logistics duties typical of a frontier post, and the fort saw renewed military use during periods of border unrest, including service during the Mexican Revolution era when U.S. forces used it to help secure the crossing and support cross-border patrol operations. The post was abandoned and reactivated more than once over its history as border conditions changed. In the twentieth century the fort grounds passed into municipal ownership and today function as Fort Duncan Park, a city park operated by Eagle Pass that preserves several restored fort-era buildings, including former officers quarters, now used to house a small museum interpreting the post's military and border history. The park's grounds serve present-day functions as public recreation space, picnic and event areas, and a heritage-tourism stop, so the site's use has shifted from active military garrison to a combined municipal recreation and small museum facility, with the surviving structures repurposed for exhibits and community use rather than active service.