Depending on timing, your tax bill will either be issued at a reduced amount, or a refund may be issued by the county.
Suffolk County: The grievance is filed in May and will affect the next tax bill, issued in December. If the entire tax bill is over-paid by the time a reduction is granted and processed, a refund will be issued from the Suffolk County Treasurer’s office.
Nassau County: Since Nassau’s filing date is far in advance of the first tax bill to be affected, the assessment rolls may be corrected beforehand. Your affected tax bill would be issued at the lowered assessment and a refund would not be necessary.