South Texas is a region of the U.S. state of Texas that lies roughly south of, or beginning at, San Antonio. The southern and western boundary is the Rio Grande River, and to the east it is the Gulf of Mexico. The population of this region is about 3.7 million. The southern portion of this region is often referred to as the Rio Grande Valley. The eastern portion along the Gulf of Mexico is also referred to as the Coastal Bend.
There is no defined northern boundary, although it is believed to be at the city of San Antonio and from an east to west line extending from the Rio Grande near Maverick County to the Gulf of Mexico, but turning southeast at or near Lavaca County, and continuing towards the Gulf of Mexico to separate it from East Texas and Southeast Texas. The Rio Grande serves as the western and southern boundaries and separates Texas from Mexico. The eastern portion of South Texas is bordered by the Gulf of Mexico.
South Texas is well-known for a strong Hispanic, primarily Mexican American and Tejano (the Spanish term for Texan) influence, due to its proximity to Mexico. However, a large percentage of Tejanos [Tejas was a province of Spain] and Mexicans living in South Texas are descended from the Spanish/Sephardic Jewish-Converso settlers of New Mexico [Onate Expedition, 1598]. These families have resided in North America for hundreds of years. This migration occurred and has been ongoing since the late 1500s in New Mexico and the early 1700s in South Texas. The long-disputed U.S. annexation of South Texas and the land grabbing of the Spanish Land Grants is a sore point among those descended from the Spanish colonial settlers. After the Mexican American War, Mexicans/Tejanos were persona non grata in Texas and at times were killed or driven from their ancestral lands. (Library of Congress, Microfiche 7906177, also google a related article "Our Secret Heritage"). The Treaty of Guadalupe Hidalgo in the 1840s, failed to secure land belonging to the Hispanic settlers. The disputed area is between the Nueces River south of San Antonio and Corpus Christi, and the King Ranch and the Rio Grande River. Not recognized by Mexico nor the United States, The Republic of the Rio Grande was established in 1838. It's capital was Laredo, Texas until 1847.