An existing district may be enlarged in the same manner as a district may be originally organized pursuant to the provisions of this act, except that a petition for the enlargement of an existing district shall be signed by at least one-third (1/3) of the qualified voters in the area of the proposed extension to this existing district, as shall be determined by the voters who voted in the last general election next preceding the filing of the petition for enlargement; and shall bear the indorsement of the board of the existing district certifying that the proposed enlargement is desirable.
Idaho Code § 42-3120