"About four years ago, Civic Space Labs commissioned me to provide them with a freely available database of US ZIP code centroids. For a while, it was hosted on their site, but at some point the link was broken. Since then, I’ve gotten about an email a month from people looking for the database.
For future reference, the free US ZIP code centroid database is now hosted here on the Mapping Hacks site. From the README:
The ZIP code database contained in ‘zipcode.csv’ contains 43204 ZIP
codes for the continental United States, Alaska, Hawaii, Puerto Rico,
and American Samoa. The database is in comma separated value format,
with columns for ZIP code, city, state, latitude, longitude, timezone
(offset from GMT), and daylight savings time flag (1 if DST is observed
in this ZIP code and 0 if not).
This database was composed using ZIP code gazetteers from the US Census
Bureau from 1999 and 2000, augmented with additional ZIP code information
from the Census Bureau’s TIGER/Line 2003 data set. Timezone information
was added using cartographic data sets from nationalatlas.gov. The
database is guaranteed to exclusively contain information gathered from
sources in the public domain, and thus be legal to redistribute.
The database is believed to contain over 98% of the ZIP Codes in current
use in the United States. ...
The database and this README are copyright 2004 CivicSpace Labs, Inc.,
and are published under a Creative Commons Attribution-ShareAlike
license, which requires that all updates must be released under the same
This could come in handy...