The 2025 County Adjacency File is a national pipe delimited text file. The list is sorted by County GEOID, and the 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:

• Counties are considered adjacent if they share an edge or have a point-to-point connection.
• Starting with the 2025 product year the ‘Length’ field is included showing the length, in meters, of the shared boundary edges of the neighboring counties. If the neighbors have a point-to-point connection, then the length will be zero.
• Each relationship with a neighboring county is represented as a new data row. A county that is adjacent to two other counties will be listed twice.
• Relationships are listed in both directions. If county ‘12345’ is adjacent to county ‘67890’, then this will appear twice in the file. It will appear once with ‘12345’ listed first as the primary GEOID and then again with ‘67890’ listed first as the primary GEOID.
• 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.
• Starting with the 2025 product year, counties will no longer be listed as adjacent to themselves. Counties with no adjacency to other counties will be listed with blank values for the adjacent county fields.