This is a map of Colorado counties as they appeared until November 15, 2001, when Broomfield County was created from portions of Adams, Boulder, Jefferson and Weld counties.
This map uses azimuthal equidistant projection, centered on (−105.7167, 39.1333) (degrees latitude, longitude).  The area outside Colorado is transparent, so it should look nice on non-white backgrounds.
The data I used is apparently accurate to 0.000278 degrees, or about 100 feet.  The coordinates in this map are in decameters.

This map is probably not eligible for copyright.  Just in case, I release my own contributions to the public domain.
Own work using: nationalatlas.gov County Boundaries, 2000 data set, specifically co2000p020.tar.gz.  I used shpdump to extract the Shapefile.  See the talk page for more details.
David Benbennick