Notice of the hearing shall be given by posting a notice thereof in three public places within the proposed improvement district, by publishing the notice once a week for two weeks in some newspaper published in the county in which the office of the district is situtated, and by mailing a copy thereof to the last known address of all the owners of lands in the improvement district, as such addresses appear in the formation petition.

The notice shall be posted and mailed not less than 20 days prior to the date set for the hearing.