The FIPS Code Hierarchy: Nation → State → County → Tract

FIPS geographic codes are hierarchical — each level is a subdivision of the level above, and the identifier at each level is built by appending digits to the parent's code. This design means that for any geography in the US, its FIPS code tells you exactly where it fits in the political and administrative structure. Our FIPS explainer covers the basics; this article goes deeper into the full hierarchy.

The levels, from top to bottom: Nation (no code needed) → State (2 digits, e.g., 53 for Washington) → County (5 digits = state + 3-digit county, e.g., 53033 for King County) → Census Tract (11 digits = county FIPS + 6-digit tract, e.g., 53033010100) → Block Group (12 digits = tract + 1 digit) → Block (15 digits = block group + 3 digits). The Census Bureau calls the full concatenated string a GEOID. At the county level, GEOID = FIPS code.

Metropolitan Statistical Areas and Congressional Districts are different — they don't nest within this county hierarchy in the same way. An MSA like the Seattle-Tacoma-Bellevue MSA (42660) is defined as a group of counties; its code doesn't encode a parent geography. Congressional districts like WA-07 are state subdivisions keyed to a state abbreviation + district number, and they don't align with county boundaries (a CD can split a county). These are overlay geographies rather than subdivisions.

For most federal statistical work, the county level is the sweet spot — small enough to capture meaningful local variation, large enough that every major federal agency publishes data at that granularity. Sub-county geographies (tracts, block groups) require working with the Census Bureau's TIGER/Line files and the ACS, which doesn't publish every variable at the block group level. Navigate the county level using the state pages and individual county profiles like King County.