The Washington State Guard (WSG) traces it’s history back to 1855 when the Washington Territorial legislature enacted the first law creating the organized militia. After Washington became a state it created its state militia in 1890. The Washington State Militia served in the Philippines during the Spanish American War of 1898 – 1899. The Washington State Militia was exclusively under state control until 1903 when the Washington National Guard was formed and placed under both federal and state control.

During World War One the exclusively state controlled Washington State Guard was reborn. The Third Infantry Regiment consisting of 16 companies, a medical detachment, and a machine gun company was formed in principal cities throughout Washington. After WWI the WSG was disbanded.

On 01 November 1940, over a year before the U.S. entered World War Two, the Washington State Guard was again re-established with an Infantry Brigade and two Regiments. During WWII the WSG was used to guard vital installations and to patrol the coast lines. As an invasion of the U.S. mainland became less apparent, the role shifted to disaster assistance and civil defense. In 1947 the WSG was again disbanded.

On 19 May 1960 Governor Albert Rosellini once more re-established the Washington State Guard to augment the Washington National Guard as an additional internal security force for the State and to replace the Washington National Guard when the latter is inducted into active federal service. The WSG has been serving continuously since then supporting the Washington Military Department in a variety of missions and assignments.