The main area code, 512, was one of the original area codes established in October 1947. At the time, it covered most of the south-central portion of Texas, from the Gulf of Mexico to the Mexican border. Besides Austin, it included San Antonio, Corpus Christi, Brownsville, Harlingen and McAllen.
Despite the presence of both San Antonio and Austin, 512 remained unchanged for 45 years. Finally, in 1992, the western part of its territory, including San Antonio, was split off as area code 210, making 512 the last of Texas' original four area codes to be split. On February 13, 1999, it was reduced to its current size when the southern portion (including Corpus Christi) was split off into 361.