San Ygnacio (Ignacio), the oldest town in Zapata County, is on the Rio Grande and U.S. Highway 83, thirty miles south of Laredo and fourteen miles northwest of Zapata. It was settled in 1830 by former residents of Revilla (now Nuevo Guerrero, Tamaulipas) under the leadership of Jesús Treviño. The site was in the southwest corner of the original Hacienda de Dolores, a grant made in 1750 by Col. José de Escandón to José Vázquez Borrego, and was named for the patron saint of Guerrero, Saint Ignatius Loyola. In 1830 Treviño built a sandstone home, known as Fort Treviño, 100 by 140 feet. José Villarreal placed a sundial at the home in 1851; the timepiece has become a tourist attraction.
San Ygnacio became a center of trade by the mid-1800s, and the town was the scene of several border skirmishes throughout the years. During the Civil War Confederate troops fought followers of Juan N. Cortina there. In 1890 revolutionary opponents of Mexican president Porfirio Díaz led raids into Mexico from San Ygnacio. And on June 15, 1916, troops of President Venustiano Carranza raided the United States border and fought a United States Cavalry unit there.
During the early 1900s San Ygnacio had several general stores, a post office, and a drugstore. In 1908 the population was 198. It increased to 400 by 1931 but dropped to 225 by the late 1940s. The town was used in the filming of Viva Zapata in 1951. San Ygnacio was scheduled to be purchased and abandoned with the construction of Falcon Dam (see INTERNATIONAL FALCON RESERVOIR), but in April 1951 several hundred residents petitioned to have their lands excluded from condemnation actions on the grounds that their townsite was sufficiently high above the maximum reservoir surface line to be safe from floods, since the floods of 1865, 1885, 1899, 1900, 1932, and 1948 had never reached any part of the community. The request was granted, but the great flood of 1954 caused widespread damage.
In 1972 the town was listed in the National Register of Historic Places, and a state historical marker commemorates the Treviño home. The historic district had thirty-six stone buildings constructed in the same style as those of old Revilla, now flooded by Falcon Dam. San Ygnacio is the last South Texas community to exhibit such a large collection of the once-numerous sandstone structures built in the middle and late nineteenth century. Many of the homes have been restored, and in 1982 the La Paz Museum was opened as the official Zapata County museum on the campus of the Arturo L. Benevides Elementary School, which was built in 1967 and enlarged in 1981. The museum houses a certified Regional Heritage Resource Center. The post office, established in 1876 by first postmaster Fernando Uribe, is now housed in the historic Trinidad Uribe home, built in 1874 and restored in 1984 by María Eva Uribe Ramírez. A large Catholic church was damaged by fire in 1990. In 1990 San Ygnacio had a population of 895. A dozen or so businesses were on the highway outside the historical area.