The 2010 county adjacency file is a national, tab delimited text file.  The list is sorted by County GEOID and then neighboring counties are sorted by Neighbor GEOID within each county.  The Island Areas appear at the end of the list.

The table below provides the layout of the county adjacency file:

• In some instances the boundary between two counties may fall within a body of water, so it seems as if the two counties do not physically touch.  These counties are included on the list as neighbors.
• Every county has itself listed as a neighboring county.