The Congress of the United States, on October 21, 1940, amended the National Defense Act to authorize local ad interim defense units during the absence of the National Guard in federal service. By the end of 1940 173 companies, comprising approximately 500 officers and 6,000 enlisted men, had been unofficially organized in Texas. On February 10, 1941, the Forty-seventh Legislature authorized the Texas Defense Guard. The name was changed to Texas State Guard in May 1943. The state's emergency appropriation of $65,000 for the guard in 1941 was supplemented by city and county donations, as well as by individual and group contributions. The governor served as commander in chief, while the state adjutant general, appointed by the governor, acted as the administrative head. Fifty battalions were planned and activated to protect public utilities, transportation arteries, and war plants; to maintain law and order; to suppress subversive activities; and to repel invasion if necessary. Battalions consisted of four to six lettered companies with headquarters and service companies and a medical detachment. For the entire state there was a camouflage company and a training and research unit. Total authorized strength was 23,075 officers and men. No pay was provided except for active duty. By regulation, each unit was to be sponsored by a civic or patriotic club. Men aged eighteen to sixty were eligible to enlist in the guard for terms of three years. Later in the war the minimum age was dropped to sixteen years, with parental consent required for the enlistment of minors. Several women's auxiliaries were organized but not officially enrolled in state service. The Austin auxiliary, composed of employees of the Department of Public Safety, trained in first aid and the operation of motor vehicles, while the Fort Worth and Corpus Christi groups helped their local guard units with paper work.
The guards drilled in schoolyards and on vacant lots with makeshift weapons until July 1941, when the War Department issued them some surplus rifles. The rifles were recalled in May 1942, and shotguns issued shortly afterward. In 1943 the shotguns were replaced with a full issue of Enfield Rifles, and the units were issued trucks, jeeps, half-tracks, and machine guns. The Eighth Service Command held training schools at Camp Bullis in September 1942, July 1943, and July 1944. In 1945 regional mobilization training schools were held. In 1946 regional rifle matches were held in Paris, Corpus Christi, Dallas, and Austin, and a statewide match was held in Austin. Units of the guard held training maneuvers at their own expense and performed several tours of active duty. Guard units were present during a riot at Beaumont, a storm at Houston, a tornado at Livingston, a train wreck in New Braunfels, and in several flood areas. They conducted searches for escaped prisoners of war, escorted a convoy of United States troops across the state to maneuver areas in Louisiana, and worked in the Texas City disaster in April 1947. During its first 6½ years of existence, a total of 94,640 individuals served in the guard. From August 1943 to May 1951 the Texas State Guard Association published The Guardsman, a monthly magazine containing information about state guard and national guard activities, as well as items of general military interest. With the return of the Texas National Guard from federal service, the TSG was disbanded by General Order 21 on August 28, 1947.
The Texas State Guard Reserve Corps, established by legislation approved on May 22, 1947, was activated by order of the adjutant general on January 26, 1948, under the command of Lt. Gen. Claude V. Birkhead. The TSGRC originally had an authorized strength of 18,000 officers and enlisted men; this figure was reduced to 12,700 in December 1950. The TSGRC, headquartered in San Antonio, was organized similarly to a division, with a commanding general, a deputy commander, a chief of staff, and a general and special staffs. The organization was composed of three brigades, each brigade having four regiments. There were, in addition, a total of thirty-six Internal Security battalions, each battalion having four companies. An advisory board, to be composed of ten TSGRC officers appointed by the governor, was established to set policy together with the adjutant general and the commanding general of the Texas National Guard. In the 1950s the Signal Corps of the TSGRC embraced 500 radio stations statewide. These provided valuable communications assistance to civil authorities and the Red Cross in times of natural disaster.
In 1961, during the Berlin Wall crisis, the Forty-ninth Armored Division and other nondivisional units of the Texas National Guard were called into federal service for a year, leaving seventy-one National Guard armories vacant. The oversight of these armories was consigned to 148 officers and 365 enlisted men in the TSGRC, who were called to active duty and formed into seventy-one Texas State Guard Security Units. The guardsmen served in this capacity until August 10, 1962, when they resumed their TSGRC status. In 1965 the Texas legislature abolished the TSGRC and reestablished the Texas State Guard, with Maj. Gen. John L. Thompson, Jr., as commanding general. The new TSG formed part of the State Military Forces, along with the Texas Army National Guard and the Texas Air National Guard (the latter two organizations being known collectively as the Texas National Guard). The minimum age for enlistment in the guard was set at seventeen and the maximum age at sixty. Individuals who reached the age of sixty, or who had served in the guard for twenty-five years, were eligible to be transferred by the governor to the TSG Honorary Reserve.
In 1968, for the first time, the legislature appropriated funds for training TSG units, allocating $11,213. The legislature that year also appropriated $240,933 for the purchase of riot-control equipment, which was made available to the TSG. Members of the TSG at this time were given training in such matters as traffic control, riot control, restoration of order, modern weapons and radioactive fallout, radiological monitoring, disaster shelters, law and order procedures for civil defense emergencies, and rescue skills. On August 14, 1970, the governor officially charged the TSG with the additional mission of assisting state and local civil defense and disaster relief officials on a voluntary basis. In addition to those members of the TSG who may be called to active duty in times of natural disaster and other emergencies, many other members of the guard frequently volunteer their assistance in relief and rescue operations. From 1965 to 1970 the headquarters of the guard was structured like that of a tactical combat unit. In 1970 the adjutant general restructured headquarters, vesting administration of the TSG in a director of the Texas State Guard. In 1992 this official, a full-time state employee, was assisted by two paid staff members. All other officials and officers, including the commanding general of the guard and the directors of personnel, operations and training, intelligence, and logistics, served in a voluntary capacity, unless called to active duty by the governor. In January 1992 the TSG had 1,528 members and an authorized strength of 3,136. Col. Thomas E. Williams was director of the guard, and Marlin Mote was commanding general. In 1994 John Bailey, a decorated Vietnam veteran, became the first African-American to serve as commanding general.