Hail / Captain Thomas William Blount House, San Augustine, Texas. Listed on the national Register of Historic Places. Historic American Buildings Survey—HABS image. – Harry L. Starnes, Public domain – Wikimedia Commons San Augustine is located in San Augustine County. About 1,920 people live here (as of 2020). Between 2010 and 2020, the population declined from 2,108 to 1,920. The region is at 113 meters above sea level. The area covers about 12.4 square kilometers. There are about 159 streets in San Augustine. The postal codes are 75972. The dialing code is 936. San Augustine is city in and county seat of San Augustine County, Texas, United States. Among other things, San Augustine has museums, schools and pharmacies. More information at visit.sanaugustinetx.com.