Eastland was elected second lieutenant of Rabb's Company F of Col. Edward Burleson's First Regiment, Texas Volunteers, on April 3, 1836, and advanced to first lieutenant when Rabb left the company and 1st Lt. W.J.E. Heard moved up to captain. At the battle of San Jacinto, according to Robert Hancock Hunter, when Sam Houston ordered that the killing of Mexican fugitives cease and that his men begin to take prisoners, Eastland responded, "Boys take prisners, you know how to take prisners, take them with the but of guns, club guns, & said remember the Alamo remember Laberde [La Bahía], & club guns, right left & nock there brains out."
Eastland enlisted in the Texas Rangers on September 5, 1836, and on December 14, 1836, succeeded Capt. M. Andrew as commander, but when he attempted to instill military discipline in their ranks the men "marched out, stacked their arms, told him to go to hell and they would go home." According to Walter P. Webb, however, Eastland yielded gracefully, maintained the rangers' respect, and continued to serve until as late as January 22, 1838. In 1839 he was elected captain of one of the three companies that campaigned against the Comanches on the upper Colorado River.
Eastland's wife, the former Florence Yellowly, died in September 1837, and in 1839 he married Louisa Mae M. Smith, the daughter of Rev. Dr. William P. Smith, a Methodist minister. By 1840 he owned 5,535 acres under survey in Bastrop County and four town lots in Bastrop. On January 31, 1840, Eastland was elected one of three land commissioners for Fayette County.
In response to the raid of Adrián Woll in 1842, Eastland raised a company that he led to San Antonio; but he arrived too late to take part in the battle of Salado Creek. He participated in the pursuit, however. His company was incorporated into Col. James R. Cook's First Regiment, Second Brigade, of Gen. Alexander Somervell's Army of the South West for the subsequent Somervell expedition. Eastland, eager for revenge for the killing of his cousin Nicholas Mosby Dawson and his nephew Robert Moore Eastland by Woll's men, chose to remain on the Rio Grande with William S. Fisher's command when Somervell ordered his expedition to return to San Antonio. Eastland was elected captain of Company B for the Mier expedition. He was taken captive with his men after the battle of Mier on December 26, 1842, and marched to the interior of Mexico. There he participated in the Texans' abortive escape attempt and was the first of the Texans to draw a fatal black bean, the only officer of the expedition to do so. In a brief private interview with Fenton M. Gibson Eastland said, "For my country I have offered all my earthly aspiration and for it I now lay down my life. I never have feared death nor do I now. For my unjustifiable execution I wish no revenge, but die in full confidence of the Christian faith." After giving his money to his brother-in-law, Robert Smith (who responded with the joyous shout that he had "made a raise!"), and sending word to his wife that "I die in the faith in which I have lived", Eastland was shot to death, on March 25, 1843. Diarist Israel Canfield, to whom Eastland was handcuffed on the march to Salado, observed with some satisfaction that Robert Smith later died at Perote Prison.
On February 17, 1844, the Texas Congress passed a bill for the relief of Eastland's family. In 1848 Eastland's remains, together with those of the other Mier victims, were moved to Monument Hill. near La Grange for reinterment. Eastland County is named in Eastland's honor.
29° 53.339, -096° 52.618
Monument Hill State Historic Site