The Eleventh Texas Infantry Battalion was technically a legion that contained both infantry and cavalry companies when first organized in Fannin County in April 1862. The unit was composed of elements of the Sixth Texas Infantry, known as Liken's Infantry and the Sabine Pass Guards, and included nearly 400 men. The original officers included Josephus S. Irvine as major, James B. Likens as major, and Ashley W. Spaight as lieutenant colonel. The men who enlisted came primarily from Jasper, Jefferson, Liberty, Newton, Orange, Rusk, Smith, and Tyler counties. The unit was known by several unofficial names including Spaight's Infantry, Irvine's Infantry, O'Bryan's Infantry, Keith's Infantry, and Marsh's Infantry. It consisted of six companies for the majority of the war and added a seventh in late 1864. Companies A and F comprised dismounted cavalry and sharpshooters.
The Eleventh Texas Infantry primarily operated in the Trans-Mississippi and was attached to Paul Hébert's Brigade and served at Sabine Pass, Beaumont, Houston, and Galveston. In March 1864 the unit was sent to the southwestern corner of Louisiana to defend against the Union Army's Red River campaign. The Eleventh Texas Infantry was involved in several engagements including: Taylor's Bayou, Texas, on September 23, 1862; Sabine Pass, Texas, on September 24–25, 1862; Galveston, Texas, on January 1, 1863; Sabine Pass, Texas, on September 8, 1863; and Calcasieu Pass, Louisiana, on May 6–10, 1864.
The men of the Eleventh Texas Infantry often fought in swampy environments and contended with mosquitoes, yellow fever, dysentery, and generally terrible conditions. Capt. W. C. Gibbs described his service as, "long hard marching and suffering from thirst under burning suns, our rations a small bit of lean beef and yellow corn bread, facing the winter's chilly blast, sleeping on the cold wet ground without tents, our lonely, dark watches on pickets, without medicine in sickness and all other privations we had to suffer." By September 1862 a terrible epidemic of yellow fever in Galveston forced quarantine of the city, and by the end of October, fourteen men in the unit died. On September 24, Company B was forced to retreat temporarily from Fort Griffin due to shelling by the Union Navy.
On May 1, 1863, the unit received orders to reinforce Gen. Richard Taylor's army in Louisiana, where they were involved in numerous skirmishes with Union soldiers. The fall and winter of 1863 was filled with sickness, famine, and freezing conditions that wreaked havoc on the unit. The unit left Camp Vermillion, Louisiana, and spent the spring of 1864 scattered, with units serving at Camp Walker near Beaumont and Sabine Pass, Texas, and Niblett's Bluff and Calcasieu Pass, Louisiana.
In November 1864 the Eleventh Texas Infantry was consolidated with Griffin's Texas Infantry Battalion, renamed the Twenty-First Texas Infantry, and sent to Galveston. The Twenty-First Infantry Regiment included field officers William H Griffin as lieutenant colonel and Felix C. McReynolds as major. In late 1864 the Twenty-First Infantry was stationed at Sabine Pass with fourteen officers and 235 men. They were briefly ordered to southwestern Louisiana but returned to Texas shortly thereafter. The unit was attached to Hébert's Division and surrendered with Gen. Edmund Kirby Smith on May 26, 1865.