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County FIPS Codes: A Plain-English Guide

Learn how five-digit county FIPS codes work, why leading zeroes matter, and how to join county data to a map reliably.

Published September 14, 2026Updated September 15, 2026By the United States County Maps editorial team

What a county FIPS code is

A county FIPS code is a five-character identifier used in federal geographic data. It combines a two-digit state code with a three-digit county code.

For example, Los Angeles County, California is 06037:

  • 06 identifies California.
  • 037 identifies Los Angeles County within California.

The combined value identifies the county nationally.

Keep the leading zeroes

Treat FIPS codes as text, not ordinary numbers. Spreadsheet software may turn 06037 into 6037, which breaks exact joins and makes the code ambiguous. Set the column type to text before importing a file whenever possible.

Names are not reliable join keys

County names repeat across states, punctuation and abbreviations vary, and county-equivalent types differ. Joining on “Washington County” alone will match many places. A five-digit FIPS code avoids that collision.

Common fields in Census files

Field Meaning Example
STATEFP Two-digit state FIPS code 06
COUNTYFP Three-digit county code within a state 037
GEOID Combined state and county code 06037
NAME Short display name Los Angeles
NAMELSAD Name with legal/statistical area description Los Angeles County

FIPS codes can change

Geographic codes are stable identifiers, but they are not permanent promises. Boundary reorganizations and changes in county-equivalent geography can add or retire codes. Connecticut’s move from former counties to planning regions is a recent example. Record the vintage of both your map and your dataset before joining them.

A safe data-joining checklist

  1. Confirm that both sources use the same geographic vintage.
  2. Store state, county, and GEOID fields as text.
  3. Pad state codes to two characters and county codes to three.
  4. Join on the five-character GEOID.
  5. Check for unmatched rows in both directions.
  6. Spot-check county-equivalents, especially in Alaska, Connecticut, and Virginia.

The tables on every state page in this atlas expose the five-digit FIPS value so you can verify map and data records without relying on a name alone.