Immediately after the filing of such petition, the department shall (1) by order fix a place and time, not less than ninety days nor more than one hundred and twenty days after the petition is filed, for hearing thereon, (2) cause notice by publication to be made of the pendency of the petition and of the time and place of hearing thereon, and (3) forthwith cause a copy of said notice to be mailed by either registered or certified mail to the county boards of each of the several counties having territory within the proposed district.