Notes on FIPS Codes

The National Institute of Standards & Technology (NIST) maintains the coding system used by the US Census and other agencies to support consistent referencing of geographic areas in the US. FIPS (Federal Information Processing Standards) codes are defined for states (2 digits), counties within states (3 digits), Census tracts within counties (6 digits), etc. These codes are concatenated to provide unique identifiers for any area down to the US Census Block level. They support efficient database matching, unlike names that may have different versions, e.g. DeSoto vs. De Soto, St. Claire vs. Saint Claire,... All of the official publications relating to FIPS codes are available from the FIPS Home Page

Changes in US County FIPS codes between 1990 and 2000 Census are documented by NIST in FIPS Publication 6-4. For example:

  • Dade County, FL (formerly 12025) changed its name to Miami-Dade (now 12086)
  • Virginia has both counties and "independent cities" with their own FIPS codes. The city of South Boston, VA (formerly 51780) was incorporated into Halifax County, VA (51083). The city of Clifton Forge (51560) was incorporated into Allegheny County (51005).
  • Yellowstone National Park (30113) was its own "county equivalent" in 1990, but was merged with Gallatin (30031) and Park (30067) Counties.
  • Broomfield County, CO (08014) was created in 2001 from parts of four neighboring counties.
Like the US Postal Service's ZIP codes, FIPS codes can include leading zero characters, and should generally be treated as TEXT fields, not numbers.

You will be joining external county-level data (typically in Excel) to Arc feature attribute tables, which will require precise matching of values in some field in the external data table to values in some corresponding field in the attribute table. records. If your external data table lacks FIPS codes, you can try creating and matching on combination STATE_COUNTY fields created by concatenating STATE and COUNTY text fields. Of you can match FIPS codes to state and county names, perhaps with Excel's VLOOKUP function.

Table Joins are easily messed up by alternate spellings, capitalizations or abbreviations, leading and/or trailing space characters, etc. Data cleanup is a lot easier in Excel than in Arc. Excel has various text functions with which you can create columns with variant spellings, etc. Excel's VLOOKUP utility lets you match a value across multiplc columns.

Here's an Excel table of county FIPS codes with variant spellings of county names.