County Adjacency File
County Adjacency File
The county adjacency file lists each county, or county equivalent, and which county, or counties, are neighboring. The file includes all 50 states, the District of Columbia, Puerto Rico, and the Island Areas (American Samoa, the Commonwealth of the Northern Mariana Islands, Guam, and the U.S. Virgin Islands).
The Census Bureau resumed production and release of the County Adjacency File product in 2023 in response to multiple requests for this product. There was no release of this product between 2010 and 2023.
2025
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File Layout
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:
| Column | Column Name | Column Description |
|---|---|---|
| 1 | County Name | 2025 county name and state abbreviation |
| 2 | County GEOID | Concatenation of the 2025 two-digit state FIPS and three-digit county FIPS codes |
| 3 | Neighbor Name | 2025 county name and state abbreviation of the neighboring county or county equivalent |
| 4 | Neighbor GEOID | Concatenation of the 2025 two-digit state FIPS and three-digit county FIPS codes of the neighboring county or county equivalent |
| 5 | Length | Length, in meters, of shared boundary edges of the neighboring counties |
Notes
- 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.