ZIP+DISTRICT is a database that links five and nine-digit USPS (United States Postal Service) ZIP Codes to 435 congressional districts and some 6,000 legislative districts, including districts for the upper and lower houses of 49 state legislatures, Nebraska's unicameral legislature, and the Council of the District of Columbia. There are six ZIP+DISTRICT data files, and each file is available for a single state or the country as a whole.

In a five-digit ZIP+DISTRICT file, each record contains one ZIP Code Service Area and one or more congressional or legislative district assignments. If a ZIP Code area is split by a district boundary, districts are listed in descending order according to the size of the area in each district. In a nine-digit ZIP+DISTRICT file, each record contains a range of ZIP+4 codes (low to high), a district assignment, and a confidence code.

For example, in the 5-digit file, the entire ZIP Code 36756 service area is located in District 7, while ZIP Code 36758 is split among three districts, Nos. 7, 2 and 3. The largest part of the ZIP Code 36758 service area is in District 7; the smallest part, in District 3. In the 9-digit file, the “plus 4” addresses in ZIP Code area 10169 that range from 10169–3110 to 10169–3126 are located in District 14. The confidence code for the assignment to District 14 is Grade 9 (census block-level accuracy).