Later Seguin was the home of Dr. John E. Park, who experimented in construction using concrete made from local materials. The nearly 100 structures—the courthouse, schools, churches, homes, cisterns, walls, etc.—made up the largest concentration of early 19th-Century concrete buildings in the U.S.
The use of concrete largely ended when the railroad arrived in 1876, bringing cheap lumber and the equipment needed for brick-making. The town had five brickworks, and the wooden buildings of downtown were completely replaced with brick by the beginning of World War I.
For almost 100 years, the town was dependent on the rich surrounding farmland and ranches. Then an oil boom came just as the Great Depression was taking down other towns and cities. Seguin could raise enough taxes to match federal grants for several 'make-work' projects. The New Deal transformed the city's public with Art Deco style City Hall, Courthouse, Jail, and fountain, as well as storm sewers, sidewalks, and three swimming pools (one for Anglos, one for blacks, one for Hispanics). The town commemorated its centennial by opening Max Starcke Park, with a golf course, picnic ares, a pavilion, a scenic river drive, and a curving dam that created one of the most beautiful waterfalls in Texas.
To preserve some of the historic character of the town, Seguin became one of the state's first Main Street cities, and the downtown district was placed on the National Register of Historic Places. Fine homes from the first half of the 20th century can be found on many streets, but the city does not have any officially designated historic residential districts.
Since the end of World War II, Texas Lutheran University has grown to about 1,400 students. The post-war era also saw industrial development, with an electric furnace mini-mill turning scrap metal into construction products, a large plant that makes electronic components for automobiles, and most recently a Caterpillar plant making diesel engines.