The Illinois National Guard comprises both Army National Guard and Air National Guard components. As of 2013, the Illinois National Guard has approximately 13,200 members. The National Guard is the only United States military force empowered to function in a state status. The Constitution of the United States specifically charges the National Guard with dual federal and state missions. Those functions range from limited actions during non-emergency situations to full scale law enforcement of martial law when local law enforcement officials can no longer maintain civil control. The National Guard may be called into federal service in response to a call by the President or Congress.
The two components are the:
When National Guard troops are called to federal service, the President serves as Commander-In-Chief. The federal mission assigned to the National Guard is: "To provide properly trained and equipped units for prompt mobilization for war, National emergency or as otherwise needed."
The Governor may call individuals or units of the Illinois National Guard into state service during emergencies or to assist in special situations which lend themselves to use of the National Guard.
The state mission assigned to the National Guard is: "To provide trained and disciplined forces for domestic emergencies or as otherwise provided by state law."
National Guard units can be mobilized at any time by presidential order to supplement regular armed forces, and upon declaration of a state of emergency by the Governor of the state in which they serve. Unlike Army Reserve members, National Guard members cannot be mobilized individually (except through voluntary transfers and Temporary Duty Assignments TDY), but only as part of their respective units. However, there has been a significant amount of individual activations to support military operations from 2001; the legality of this policy is a major issue within the National Guard.