The fact of the presentation of the petition, and the order establishing the library district and making the appointment of the five library trustees, shall be entered in the minutes of the board of supervisors and shall be conclusive evidence of the due presentation of a proper petition, and that each of the petitioners was, at the time of signature and presentation of the petition, a taxpayer and resident of the proposed district, and of the fact and regularity of all prior proceedings of every kind and nature provided for by this article and of the existence and validity of the district.