Rockdale is a city in Milam County, Texas, United States. Its population was 5,323 at the 2020 census. It is approximately 41 miles west of C…Rockdale is a city in Milam County, Texas, United States. Its population was 5,323 at the 2020 census. It is approximately 41 miles west of College Station. As a passing point of the "Camino Real" and the establishment of three missions in the area, a wooden fort was established on the south bank of the San Xavier River, to protect those missions, circa 1751. The fort was called San Francisco Xavier de Gigedo Presidio.