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Internet/Mail-Order sales and cell phones present many difficulties for the collection and distribution of traditional sales taxes. With the recent adoption of federal protocols for administering Streamlined Sales Tax and Mobile Telecommunications Sales Tax, the importance of precisely locating USPS ZIP+4 nine-digit ZIP Codes has become critical to tax agencies. Delivery point ZIP+4's must be linked to their respective taxing jurisdictions. While ZIP+4's have a definite real world geography (usually a block face, building, or PO Box), the USPS Address Information System product does not model the positional location of ZIP+4's in a geographic coordinates. This missing locational information can be discovered utilizing GIS datasets, software, and custom programming. This paper will present the use of ArcGIS 9 (including Model Builder, ArcToolbox, VBA, and Python) together with a variety of publicly available GIS data from local government to locate ZIP+4's and the taxing jurisdiction that each falls within.