Indiana offers property owners a number of deductions that can help lower property tax bills. Tax deductions subtract a certain amount from your property's Assessed Value (AV). You will need to complete and file an application for each of the deductions you wish to claim with the Porter County Auditor’s office. Generally, applications must be completed, signed and dated by December 31st in order to obtain the deduction in the immediately succeeding year. The completed deduction form along with all necessary documentation, must be filed or post marked on or before January 5th.