Two Python functions -- one to return a dictionary of U.S. county FIPS codes, another to return a JSON array of objects of county adjacency data.

county_adjacency.py

import requests
import csv
import json

def getCounties():
    "Function to return a dict of FIPS codes (keys) of U.S. counties (values)"
    d = {}
    r = requests.get("http://www2.census.gov/geo/docs/reference/codes/files/national_county.txt")
    reader = csv.reader(r.text.splitlines(), delimiter=',')    
    for line in reader:
        d[line[1] + line[2]] = line[3].replace(" County","")    
    return d

def getCountyAdj():
    "Return a list of dicts where each dict has a county FIPS code (key) and a list of FIPS codes of the adjacent counties, not including that county (value)"
    adj = requests.get("http://www2.census.gov/geo/docs/reference/county_adjacency.txt")
    adj_data = adj.text.encode("utf-8")
    reader = csv.reader(adj_data.splitlines(), delimiter='\t')
    ls = []
    d = {}
    countyfips = ""
    for row in reader:
        if row[1] and row[1] != "":
            if d:
                ls.append(d)
            d = {}
            countyfips = row[1]
            d[countyfips] = []
            "Grab the record on the same line"
            try:
                st = row[3]
                if st != countyfips:
                    d[countyfips].append(st)
            except:
                pass
        else:
            "Grab the rest of the records"
            if row[3] and row[3] != "":
                st = row[3]
                if st != countyfips:
                    d[countyfips].append(st)
    return json.dumps(ls)

Kudos for the getCounties function. Saved me some time.

just what I was looking for, thanks!