Castroville is a city in Medina County, Texas, United States. Its population was 2,954 at the 2020 census, up from 2,680 at the 2010 census. It is part of the San Antonio–New Braunfels, Texas Metropolitan Statistical Area. Castroville was founded by Alsatian-Texans, who came to Texas during the German emigration period of the mid-1800s. Most Alsatians who came to Castroville spoke Alsatian. The Alsatian culture and language are still kept alive by the residents of Castroville. Prior to 1893, Castroville was the first county seat of Medina County.