Texas State Highway 21
State Highway 21, or SH 21, runs from the Texas-Louisiana boundary east of San Augustine to San Marcos in east and central Texas. SH 21 mostly follows the alignment of the Old San Antonio Road and the El Camino Real, except for the portion between Midway and Bryan, where the Old San Antonio Road took a more northerly route, and SH 21 follows a more direct route. That section of the Old San Antonio Road is served by Texas State Highway OSR.
History
SH 21 was one of the original 26 routes proposed in Texas in 1917 along a route from St. Augustine to Gonzales. There was proposed extension southward to Karnes City by 1922, but most of it was transferred to SH 80 instead. In 1926, the terminus was shortened to Giddings. By 1943, the western terminus had been rerouted through Paige to end in San Marcos, along its current route.
In 2010, the SH 21 designation was extended along SH 80 and SH 142 to end at I-35.
Business routes
SH 21 has one business route.
Business State Highway 21-H is a Business Loop that runs through Kurten in central Texas. The road was bypassed in 2002 by SH 21.