50 ILCS 425/10

Notes issued under the provisions of this Act shall be incontestable after authentication by the treasurer and delivery to a purchaser for a valuable consideration, and in like manner and to like extent as though the same were negotiable instruments, and shall be payable only out of and from the proceeds of revenues expected and described in the proceedings authorizing the issuance of the notes, and shall so state on their face, and shall not be deemed to be an obligation of the unit of local government or school district within any constitutional or statutory limitation.