On 10 FEB 1941, the Defense Act (H.B. No. 45) authorized a volunteer militia. Volunteers from the San Antonio area were constituted as the 36th Battalion of the Texas Defense Guard. This unit remained active throughout World War II and in 1943 the 48th Legislature changed the name of the Defense Guard to Texas State Guard.

After the Texas State Guard was inactivated after the war on 28 AUG 1947 (AGTX-GO 21), the 50th Legislature re-authorized the Texas State Guard Reserve Corps on 26 JAN 1948 (AGTX-GO 4) and the unit reformed and designated the 11th Regiment.

In 1965, the unit was re-designated the 8th Military Police Group. When the Texas State Guard reorganized on 1 JUL 1993 the state defense force from South Texas was designated as the 1st Brigade and the name Alamo Guards reclaimed for the unit.

The original Alamo Guards were constituted on 2 OCT 1885 as part of the Texas Volunteer Guard.