This Calhoun County Illinois zip code (zcta) map does not show post box zip codes or
unique zip codes. These maps are designed for quick general lookup of census zip code
polygon areas. The Census Bureau does not keep up-to-date data-sets of all ZIP codes.
ZIP Code Tabulation Areas (ZCTAs™) are a new statistical entity developed by the U.S.
Census Bureau for tabulating summary statistics from Census 2000. This new entity was
developed to overcome the difficulties in precisely defining the land area covered by each
ZIP Code. Defining the extent of an area is necessary in order to accurately tabulate
census data for that area.
ZCTAs are generalized area representations of U.S. Postal
Service (USPS) ZIP Code service areas. Simply put, each one is built by aggregating the
Census 2000 blocks, whose addresses use a given ZIP Code, into a ZCTA which gets that
ZIP Code assigned as its ZCTA code. They represent the majority USPS five-digit ZIP Code
found in a given area. For those areas where it is difficult to determine the prevailing five-
digit ZIP Code, the higher-level three-digit ZIP Code is used for the ZCTA code. Also, Some
areas that are in remote regions might have PO box zip code usage.
Source U.S. Census
Many large businesses, commercial shipping companies, insurance companies, sales
people, sales marketers, travelers, trucking companies, lawyers, demographic
researchers, delivery & freight services,Realtors & real estate companies, and citizens
needing zip code information use this census information everyday.
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