State Highway 21 (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.

Quick Facts State Highway 21, Route information ...

State Highway 21
Route information
Maintained by TxDOT
Length	312.50 mi[1] (502.92 km)
Existed	April 4, 1917–present
Major junctions
West end	I-35 at San Marcos
Major intersections	US 183 / SH 130 Toll in Mustang Ridge US 290 in Paige US 77 near Lincoln US 190 / SH 6 in Bryan I-45 / US 190 in Madisonville US 287 in Crockett US 69 in Alto Future I-69 / US 59 in Nacogdoches US 96 in San Augustine
East end	LA 6 near Milam
Location
Country	United States
State	Texas
Counties	Hays, Caldwell, Bastrop, Lee, Burleson, Brazos, Madison, Houston, Cherokee, Nacogdoches, San Augustine, Sabine
Highway system
Highways in Texas Interstate US State Toll Loops Spurs FM/RM Park Rec
← SH 20 → SH 22

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SH 21 was one of the original 25 routes proposed in Texas on June 21, 1917, along a route from the Louisiana state line east of St. Augustine to Gonzales, overlaid on top of the Gonzales-St. Augustine Highway.^[2] There was proposed extension southward to Karnes City on February 18, 1918.^[3] On July 16, 1923, the terminus was shortened to Giddings, with the section south of there being cancelled.^[4] A spur, SH 21 Spur, was designated on March 19, 1930, from Milam to Hemphill. On August 1, 1930, this spur became part of SH 87. On September 29, 1933, SH 21 was extended to Lockhart. On July 15, 1935, the section from Giddings to Lockhart was cancelled, and SH 21 was rerouted though Lincoln, replacing part of SH OSR, and followed SH 44 to Giddings.^[5] On October 21, 1936, SH 21 Spur to Chireno was added.^[6] On May 18, 1937, the spur in Chireno became a loop, SH 21 Loop.^[7] On February 21, 1938, another SH 21 Spur to McMahan's Chapel was added.^[8] On April 19, 1938, the section of SH 21 from Lincoln to Giddings was cancelled, and SH 21 was extended to Bastrop, replacing part of SH OSR. On September 26, 1939, the section from Paige to Bastrop was cancelled, as it was already part of US 290. The spur and loop became Loop 34 (Chireno) and Spur 35 (McMahan's Chapel). On August 2, 1943, the western terminus had been extended to end in San Marcos, along its current route, replacing part of SH OSR.

On June 24, 2010, the SH 21 designation was extended along SH 80 and SH 142 to end at I-35.^[9][10]

SH 21 has two business routes.

Nacogdoches business route

Quick Facts Business State Highway 21-P, Location ...

Business State Highway 21-P
Location	Nacogdoches
Length	4.170 mi[13] (6.711 km)
Existed	2018–present

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Business State Highway 21-P (Bus. SH 21-P) is a 4.170-mile (6.711 km) long business route that runs through Nacogdoches in eastern Texas.^[13] The route was formed from an old section of SH 21, when the main highway was re-routed onto Loop 224 and US 59 on October 25, 2018.^[14]

Major intersections

The entire route is in Nacogdoches, Nacogdoches County.

More information mi, km ...

mi[13]	km	Destinations	Notes
0.000	0.000	US 59 / SH 21 east / Loop 224 (Stallings Drive) SH 21 west (Douglass Road)	Western terminus; road continues as SH 21 west
1.341	2.158	FM 225 west (Durst Street)	Eastern terminus of FM 225
1.803	2.902	Bus. US 59 / Bus. SH 7-N west (North Street/South Street)	Western end of Bus. SH 7-N concurrency
2.375	3.822	FM 1275 (University Drive)
2.487	4.002	FM 2259 south (Shawnee Street)	Northern terminus of FM 2259
3.043	4.897	Bus. SH 7-N east (Center Road)	Eastern end of Bus. SH 7-N concurrency
4.170	6.711	SH 7 (Stallings Drive) / SH 21 west / Loop 224 SH 21 east (Main Street)	Eastern terminus; road continues as SH 21 east
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus

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