The First Texas Cavalry, also known as McCulloch's Texas Cavalry, was organized and mustered into service on April 15, 1861. It is more commonly known by its nickname, the First Texas Mounted Rifles. Many of the regiment's original members were Texas Rangers before the start of the Civil War. Col. Henry Eustace McCulloch organized the unit and served as its first commanding officer. He was given various assignments and commands throughout the war and received a promotion to the rank of brigadier general on March 14, 1862. The men serving in McCulloch's regiment came primarily from the counties of Bastrop, Bell, Hill, Dallas, and Gonzales. As originally mustered, the regiment had roughly 1,000 men in service. With McCulloch commanding, the regiment's field officers were Maj. James B. Barry, Maj. Edward Burleson, Jr., and Lt. Col. Thomas C. Frost.
On May 9, 1861, six companies of the First Texas Cavalry Regiment serving under Col. Earl Van Dorn took part in the so-called battle of Adams Hill, also referred to as the battle of San Lucas Springs, just west of San Antonio. At Adams Hill no shots were fired as the heavily outnumbered Union forces surrendered and were allowed to march on to San Antonio. On November 1, 1861, one company of the First Texas Cavalry Regiment took part in a skirmish with Indians on the Peosi River, which is a branch of the Red River. The company, commanded by Capt. James B. Barry, killed ten Indians and wounded the remaining two during the skirmish. As the First Texas Cavalry, the regiment saw no further action. In April 1862 the regiment was reduced to a battalion with five companies. It then officially became the Eighth Cavalry Battalion.