Answer: They were mostly populated with white Americans
Moses Austin was the first colonist who went about colonizing this area of Texas. He discussed this with Governor Antonio Martinez who allowed 300 American families to settle in Texas. Moses Austin died before he could carry out his plans, but these were continued by his son, Stephen F. Austin.
Stephen F. Austin decided that the region should be that between the Colorado and the Brazos River, as it has mild climate and plenty of good soil and natural resources.
Austin advertised for settlers to come to his colony. Many did, and the settlers became known as the "Old Three Hundred." Most were white Americans from Alabama, Arkansas, Louisiana, Missouri, and Tennessee. However, settlers had to become citizens of Mexico and convert to Roman Catholicism.