Payables / Procurement / Receivables Forms ACH Enrollment Form (PDF 4.38 MB) W-9 Blank Fillable Form (PDF 137.51 KB) W-9 Supplier Letter (PDF 2.09 MB) W-9 for Washington County (PDF 59.04 KB) Washington County IRS Tax Exemption Letter (PDF 49.02 KB) Washington County Oregon Business Registry Resale Certificate (PDF 34.88 KB) Location Finance 155 N First Avenue Hillsboro, Oregon 97124 Hours and directions View all county locations