Ripley Allen Arnold, United States Army officer, the son of Willis Arnold, was born at Pearlington, near Bay St. Louis, in Hancock County, Mississippi, on January 17, 1817, and was appointed to the United States Military Academy at West Point in 1834. He was said to have been a talented song writer whose compositions were popular at the academy. He reportedly fought a duel at an infamous drinking establishment, Benny Haven's, while still a cadet. He graduated thirty-third in his class and was assigned to duty as a second lieutenant of the First Dragoons in Florida on July 1, 1838. On February 1, 1839, he was promoted to first lieutenant. He and Catherine Bryant eloped on her fourteenth birthday (August 26, 1839) and were married in Pass Christian, Mississippi. They had five children.
Arnold was brevetted captain on April 19, 1842, for gallant conduct in the Seminole War and major on May 9, 1846, for his role in the battles of Palo Alto and Resaca de la Palma. He served under Gen. William J. Worth through the battle of Monterrey. He was then transferred to the army of Gen. Winfield Scott and took part in the battle of Molino del Rey and the capture of Mexico City in 1847. Arnold was promoted to captain on May 11, 1846, and served as assistant quartermaster until March 10, 1847.
He was given command of Company F of the Second Dragoons after the Mexican War and ordered to northern Texas to establish a military post "at or near the confluence of the West Fork and the Clear Fork of the Trinity River." In the latter part of May 1849, after locating a suitable site for the new camp, he left Fort Graham with forty-two dragoons and proceeded to the Trinity, where, on June 6, 1849, he established Camp Worth, which he named after his former commander, who had recently died of cholera in San Antonio. With a portable, horse-powered sawmill his company constructed a barracks, a mess hall, a commissary, an infirmary, stables, and a smithy. Camp Worth, later named Fort Worth, was completed by mid-winter of 1849, and in 1850 Arnold's wife and five children joined him from Washington, D.C. Two of the couple's daughters died shortly after their arrival and were buried near the fort.
Arnold and his company returned to Fort Graham on June 17, 1851. He was detached to duty in Washington in 1852 but returned to command of Fort Graham in 1853. During this period his company launched a preemptive strike against a war party led by Comanche chief Jim Ned. They pursued the raiding parties of Jim Ned and Feathertail into what is now Palo Pinto County, where they defeated the Indians. Jim Ned was killed in the fighting, and Comanche raiders never ventured as far east as Tarrant County again.
Arnold was known as a strict disciplinarian. When a soldier stole a hog from a nearby farm, Arnold ordered that he remain tied for several hours in front of the officers' quarters in the July sun with the remains of the slaughtered animal hung around his neck.
Arnold was killed at Fort Graham on September 6, 1853, by Josephus Murray Steiner, in an exchange of shots. Civil and military authorities disputed jurisdiction in the case, and Steiner was ultimately acquitted by both court-martial and a civil jury. He was represented by future governor Richard Coke and future Confederate general William H. Parsons, who established that Arnold had been procuring United States government horses under questionable circumstances and selling them for his own profit. Steiner's attorneys claimed that their client had known of this practice and planned to expose it. One witness swore that Arnold had threatened, "I will put him out of the way; he shall not give evidence against me." Arnold was first buried at Fort Graham, then disinterred and removed to Fort Worth, where he was buried in the Pioneer's Rest Cemetery, within a mile of old Fort Worth and near the graves of his two infant daughters. He was said to have received the first Masonic rites ever performed in Fort Worth. His diary and personal papers were destroyed by fire at the Fort Worth home of one of his granddaughters.