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| State Highway 21 (Texas) | |
|---|---|
| State | TX |
| Type | SH |
| Route | 21 |
| Direction a | West |
| Direction b | East |
| Terminus a | San Marcos |
| Terminus b | Henderson County |
| Counties | Hays County, Travis County, Bastrop County, Lee County, Fayette County, Colorado County, Jackson County, Matagorda County, Wharton County, Colorado County, Austin County, Brazoria County, Stanley County |
State Highway 21 (Texas) is an east–west state highway in the U.S. state of Texas that connects San Marcos and rural areas in eastern Texas. The route follows corridors associated with the El Camino Real de los Tejas National Historic Trail, passing near landmarks such as the San Marcos River and the Stephen F. Austin State University region. It serves as a connector between multiple state and U.S. highways and traverses varied landscapes from the Edward Plateau margins to the Gulf Coastal Plain.
SH 21 begins at an intersection with Interstate 35 in San Marcos, proceeding eastward toward Bastrop where it intersects U.S. Route 290 and crosses the Colorado River. The highway continues through Caldwell County and near Gonzales, intersecting U.S. Route 183 and U.S. Route 77 corridors. East of Gonzales County SH 21 parallels alignments linked to the San Antonio–Nacogdoches Road and crosses routes connecting to Victoria and Houston via U.S. Route 59 and State Highway 35. The highway provides access to El Camino Real de los Tejas National Historic Trail sites, regional parks, and agricultural communities in Fayette County and Jackson County before terminating near rural junctions that feed toward Henderson County road networks.
Along its length SH 21 intersects major arteries including Interstate 10, U.S. 77 Alternate, and several state highways such as State Highway 80, State Highway 71, and State Highway 6. The route serves small cities and towns with ties to historical figures like Stephen F. Austin, Sam Houston, and Mirabeau B. Lamar, and provides proximity to sites associated with the Texas Revolution and the Mexican–American War era.
The corridor traces historic paths used during Spanish colonization and early Republic of Texas settlement, echoing the route of the El Camino Real de los Tejas National Historic Trail established during the Viceroyalty of New Spain. In the early 20th century, state highway planning during the Texas Highway Department era designated numbered routes linking San Marcos, Bastrop, and east Texas communities; these developments paralleled infrastructure investments during the administrations of Governor Miriam A. "Ma" Ferguson and Governor James V. Allred. The alignment was refined with paving projects funded through federal programs influenced by the Federal Aid Highway Act frameworks and by coordination with U.S. Route designations implemented under the American Association of State Highway Officials.
Mid-century modifications responded to increasing traffic from interstate connections and the growth of Austin and Houston metropolitan areas. The route was realigned in places to improve safety near river crossings and to bypass downtowns of towns such as Gonzales and Bastrop, reflecting planning practices from agencies like the Texas Department of Transportation. Preservation efforts for historic waypoints along SH 21 led to collaborations with organizations such as the National Park Service and the Texas Historical Commission.
The highway intersects numerous significant routes, providing regional connectivity: - Western terminus: I‑35 at San Marcos. - Junctions with U.S. 290 near Bastrop. - Crosses U.S. 183 near Gonzales. - Interchange with U.S. 77/U.S. 59 corridors facilitating access to Victoria and Houston. - Intersections with SH 80, SH 71, SH 6, and connections to I‑10. - Eastern termini and major rural junctions provide links to county roads toward Henderson County and nearby state routes feeding into Beaumont and Lufkin corridors.
Several business loops and spurs diverge from SH 21 to serve downtown districts and historic centers. Business routes provide direct access to municipal centers including Bastrop Historic District, Gonzales downtown, and smaller county seats such as La Grange and Columbus. These business designations preserve commercial traffic patterns connecting to Texas State Highway Loop designations and local county road networks managed in coordination with the Texas Department of Transportation.
Planned improvements along SH 21 focus on safety enhancements, capacity upgrades, and historic preservation tied to the El Camino Real de los Tejas National Historic Trail designation. Projects under consideration involve interchange improvements near I‑35 and U.S. 290 to accommodate growth from the Austin–Round Rock metropolitan area and San Antonio–New Braunfels metropolitan area expansions. Funding proposals reference state transportation plans administered by the Texas Department of Transportation and may include multimodal elements to link with Amtrak corridors and regional transit initiatives promoted by metropolitan planning organizations such as the Capital Area Metropolitan Planning Organization.