Oregon Revised Statutes Public Lands § 271.220

All objections to the petition shall be filed with the clerk or auditor of the city or town within 30 days from the filing of the petition, and if not so filed shall be conclusively presumed to have been waived. The regularity, validity and correctness of the proceedings of the city governing body pursuant to ORS 271.180 to 271.210, shall be conclusive in all things on all parties, and cannot in any manner be contested in any proceeding whatsoever by any person not filing written objections within the time provided in this section.