The Illinois Promissory Note and Bank Holiday Act establishes the procedure for closing the bank on a single occasion. 205 ILCS 630/17(c). To close on a particular day, the board of directors must adopt a resolution authorizing the closure, you must send a copy of the resolution to the Department of Financial and Professional Regulation, and you must post notices for at least three weeks in your main office and all branches. If it turns out that you are able to keep some branches open, that will not violate the Act; “no bank in this State, which by law or custom is entitled to remain open or to close for the whole or any part of any day selected by it to remain open or to close, is compelled to close, or to remain open for the transaction of business or to perform any of the acts or transactions aforesaid except at its own option.” 205 ILCS 630/17(f). (The IDFPR has confirmed this interpretation.)