2023 back tax sale August 28th. Posted on August 16, 2023August 16, 2023 the annual Grundy County back tax sale will be Monday August 28th starting at 10am on the first floor of the courthouse in Trenton. anyone who is interested in bidding on properties should contact the collectors office. Barb HarrisCollector / Treasurer Brenda OrndorffDeputy Collector / Treasurer