The Illinois Army National Guard was originally formed in 1712 as a colonial French militia.

The militia worked under British sovereignty in the mid-eighteenth century, until the American Revolutionary War, when in 1779 Colonel George Rogers Clark, with 200 frontiersmen, of the Illinois Regiment, Virginia State Forces, from Kaskaskia, captured Fort Sackville from British Colonel Henry Hamilton and his military forces.

Following the American Civil War, the state forces were reorganized under the command of Arthur C. Ducat, who became the first major general of the statewide Illinois militia.

It was inducted into Federal Service during the Korean War but on its release the Governor of Illinois declined to support it, citing budgetary considerations.

More specifically, United States Department of Defense policy was that no Guardsman will be involuntarily activated for a total of more than 24 months (cumulative) in one six-year enlistment period.