Notice of the public hearing shall be mailed to all parties in interest at least 10 days before the hearing. “Parties in interest” shall be defined as the petitioner, the Clerk of any municipality whose boundaries are within 1,000 feet of any lands included in the petition and the owners of all lands included in the petition and all lands lying within 250 feet of lands included in the petition. The failure to give any notice to any property owner shall not invalidate the action taken by one of the aforementioned bodies.