Try this Census page for a listing of FIPS codes down to county level:
http://eire.census.gov/popest/archives/files/fips.txt
Charles Trainor
Land Use Resources Director
Community Planning Association
800 S. Industry Way Suite 100
Meridian, ID 83642
208.855.2558 voice
208.855.2559 fax
ctrainor@compassidaho.org
www.compassidaho.org