Is the Rio Grande border between Texas and Mexico?

Yes, the Rio Grande border is between Texas and Mexico. The Rio Grande, also known as the Río Bravo del Norte in Mexico, forms a natural border between the U.S. state of Texas and the Mexican states of Chihuahua, Coahuila, Nuevo León, and Tamaulipas. The river flows for approximately 1,250 miles (2,010 km) from its source in the Rocky Mountains in Colorado to the Gulf of Mexico.