The community was officially established 170 years ago specifically on March 27, 1849, when the U.S. government set up the permanent Fort Duncan Military post on the East Bank of the Rio Grande River.

Prior to the establishment of Fort Duncan, a temporary settlement called Camp Eagle Pass was located at the site at the start of the Mexican-American War in 1846. Fort Duncan was then established and named in honor of Mexican-American War hero, James Duncan. History records show that the establishment of the Fort Duncan brought an increase of traffic through the area leading to the settling and establishing of Eagle Pass around that time.

Eagle Pass was the first American settlements on the Rio Grande and has had many historical significant occurrences during its time. One of those events goes back to 1865 when Fort Duncan was held by the Confederacy during the American Civil War. On July 4, 1865, General Joseph O. Shelby, en route to offer his troops' service to Maximilian in Mexico, stopped at Fort Duncan and buried in the Rio Grande the last Confederate flag to have flown over his men. The rancher and gunfighter King Fisher also lived in Eagle Pass and reigned the territory for numerous years until his ambush and murder in San Antonio in 1884. During the 17 decades of existence, Eagle Pass has gone through so many changes and continues to grow as every year passes. 

In 1933 Fort Duncan closed down and eventually, the City of Eagle Pass was allowed to develop and maintain the old post as a public park, eventually, the property was handed over to the city.

Now called Fort Duncan Park, the site was listed in the National Register of Historic Places in 1971. The City of Eagle Pass continues maintaining the area and in recent years have concentrated efforts in embracing the history of Eagle Pass including the Fort Duncan Park area and its historical significance.