Census Bureau Data and FIPS Codes: A Researcher's Guide

The Census Bureau is both the primary publisher of FIPS geographic codes and the largest producer of county-level data products that use them. Understanding how Census data products are organized around FIPS codes is foundational for anyone working with US government data. Our federal data guide covers the full landscape, but the Census Bureau deserves special attention.

The Bureau's flagship statistical product for small-area data is the American Community Survey (ACS), which publishes 1-year and 5-year estimates for every geographic level from the nation down to Census blocks. All of these are identified by FIPS codes and GEOIDs — a GEOID is simply the full FIPS code hierarchy concatenated into a single string. For a county, the GEOID and the 5-digit FIPS code are identical. For a Census tract in King County, WA, the GEOID is 530330101 — state (53) + county (033) + tract (0101).

The Census Bureau also publishes Decennial Census counts, Population Estimates Program (PEP) data, the County Business Patterns (CBP), and the Longitudinal Employer-Household Dynamics (LEHD) data — all using county FIPS codes as the primary geographic identifier. When working with the Census API, you'll specify geography using FIPS codes: for=county:033&in=state:53 returns data for King County.

One important distinction: the Census Bureau maintains the ANSI/FIPS code list and publishes updates when counties change (e.g., South Dakota's Shannon County was renamed Oglala Lakota County and renumbered from 46113 to 46102 in 2015). Always verify you're using current codes when working with historical data. The county codes guide and individual state pages reflect the current authoritative list.