From the Minneapolis Fed - https://www.minneapolisfed.org/community/teaching-aids/cpi-calculator-information/consumer-price-index-1800
Distances between County that are within 100 miles
Distances between County that are within 50 miles
Distances between County that are within 25 miles
Unique identifier is  county
Census Gazetteer County file
by Jean Roth , jroth@nber.org , 29 Mar 2016
Source File: counties.txt
Source File URL: http://www2.census.gov/geo/docs/maps-data/data/gazetteer/counties.zip
Source Page: http://www.census.gov/geo/maps-data/data/gazetteer1990.html
counties1990 set up by Jean Roth , jroth@nber.org , 29 Mar 2016