20 ILCS 1805/40
Except where otherwise specified herein, all officers now in active service or hereafter appointed, shall hold their respective commissions until they are vacated by resignation or retirement, or by acceptance of another commission in the State military service, or by sentence of a general courts-martial, approved finding of a board of officers under Section 42, Article VIII, approved finding of a board of officers convened pursuant to federal regulations in which the board recommends withdrawal of federal recognition of the officer's commission, or terminated under Section 43, Article VIII hereof. Federal recognition with commission in the National Guard of the United States is established as a requirement for holding commission in the active National Guard of Illinois; the commission of an officer in the National Guard of Illinois will be terminated upon failure to obtain or retain Federal recognition.
20 ILCS 1805/40