A FIPS code is a standardized numeric label the federal government assigns to every state, county, and smaller geographic area in the United States, so different agencies and databases can point to the same place without confusion. FIPS stands for Federal Information Processing Standards. If you’ve ever programmed a weather radio, looked up flood zones, or pulled Census data, a FIPS code was doing the work of tying that information to a specific location.1National Bureau of Standards. FIPS PUB 5-2 – Codes for the Identification of the States, the District of Columbia and the Outlying Areas of the United States, and Associated Areas
The codes are now formally maintained under ANSI/INCITS standards rather than the original FIPS publications, but the numeric values didn’t change when the standards were reissued, and everyone still calls them FIPS codes in day-to-day use.2National Institute of Standards and Technology (NIST). Replacement Standards for Withdrawn FIPS on Geographic Codes
How the Digits Are Built
FIPS codes nest. You start with the broadest area and add digits as you zoom in, so a longer code always contains the shorter ones inside it.
States and Counties
Every state and the District of Columbia has a unique two-digit code. California is 06, Texas is 48, New York is 36.3Federal Communications Commission (FCC). Federal Information Processing System (FIPS) Codes for States and Counties Counties get a three-digit code, but the three-digit number alone is ambiguous because forty-nine counties across the country end in 001. Attach the state code to the front and you get a unique five-digit county identifier. Harris County, Texas is 48201: 48 for Texas, 201 for Harris County.4United States Census Bureau. Understanding Geographic Identifiers (GEOIDs)
Census Tracts and Blocks
Below the county, the Census Bureau adds a six-digit tract number, producing an 11-digit identifier. Census Tract 2231 in Harris County is 48201223100. A four-digit block number goes on the end for the finest level of detail, making a 15-digit code. The first digit of that block number also identifies the block group, so no separate block-group code is needed. Block 1050 in that same tract is 482012231001050.4United States Census Bureau. Understanding Geographic Identifiers (GEOIDs)
FIPS Codes and ZIP Codes Are Not the Same
A ZIP code is a postal delivery route. It follows mail carrier paths and can straddle county or even state lines. A FIPS code follows political and administrative boundaries that nest cleanly. Because of that mismatch, records organized by ZIP (like a lot of health data) don’t line up neatly with records organized by county or tract (like most demographic data). The Department of Housing and Urban Development publishes crosswalk files that allocate data between ZIP codes and Census geographies using residential address ratios, and researchers lean on them constantly.5HUD USER. HUD USPS ZIP Code Crosswalk Files
Where You’ll Actually Run Into One
Emergency Alerts
When a severe thunderstorm warning or AMBER Alert goes out, a FIPS code decides who hears it. NOAA Weather Radio and the Emergency Alert System use Specific Area Message Encoding (SAME), which embeds a six-digit FIPS-based code to target alerts to specific counties. A weather radio with county-specific alerting has to be programmed with your county’s code so it only sounds for threats in your area.6National Weather Service. FIPS Codes for NWR SAME Input FEMA’s Integrated Public Alert and Warning System uses the same geographic framework to push alerts to phones, radio, and television.7FEMA. Integrated Public Alert and Warning System
Disaster Declarations
When the president declares a major disaster, FEMA tags the affected areas using a place-code system built on three-digit county FIPS codes.8FEMA. Disaster Declarations Summaries That tagging is what determines which communities are eligible for individual assistance, public assistance, and hazard mitigation grants.9FEMA. Hazard Mitigation Assistance Program and Policy Guide
Census Data
The Census Bureau organizes almost everything it publishes by FIPS-coded geography. Population estimates, American Community Survey tables, and decennial results all use the codes as the primary geographic key, which is why researchers geocode street addresses to FIPS codes when they want tract-level demographics for a public health study, a market analysis, or a policy report.
Environmental Screening
The EPA’s EJScreen tool works at the census block group level, combining pollution indicators with demographic data. Because block groups sit inside tracts inside counties, the tool relies on the hierarchical FIPS structure to move data cleanly between levels and produce environmental justice indexes for every block group in the country.10EPA (U.S. Environmental Protection Agency). Technical Documentation for the Environmental Justice Screening and Mapping Tool EJSCREEN
Flood Insurance
The National Flood Insurance Program embeds the five-digit state-and-county FIPS code alongside FEMA’s community numbers to link a floodplain to the jurisdiction that manages it. For a property in a flood zone, that code is part of what connects the parcel to the correct map panel and local floodplain authority.
Codes Can Change
FIPS codes are not permanent. Counties get renamed, boundaries shift, and new jurisdictions form. The Census Bureau records each change, with legal effective dates, in its Geographic Boundary Change Notes.11United States Census Bureau. Geographic Boundary Change Notes
Shannon County, South Dakota is the clearest recent example. It was renamed Oglala Lakota County, and its county code changed from 113 to 102; every subdivision inside it got new codes as well.12United States Census Bureau. 2015 Table and Geography Changes Anyone running an analysis that spans the change year has to account for it, or the same place will look like two different counties in the data.
How to Look Up a FIPS Code
The Census Bureau maintains the fullest set of lookup resources. Its reference pages list codes for states, counties, county subdivisions, and places as downloadable spreadsheets organized by hierarchy.13United States Census Bureau. American National Standards Institute (ANSI), Federal Information Processing Series (FIPS), and Other Standardized Geographic Codes Population estimates pages carry similar downloads by state and county.14United States Census Bureau. 2022 Population Estimates FIPS Codes
For a single address, the free Census Geocoder returns the matching state, county, and tract codes.15Census Bureau. Census Geocoder Use a full street address if you can. Looking up by city name or ZIP can give ambiguous results, because both can cross county lines.
For bulk work, the Census Geocoding Services API accepts single addresses or batch files and returns FIPS codes when the return type is set to “geographies.” It supports one-line address searches as well as split-field queries with street, city, state, and ZIP, so it drops into most data pipelines without much fuss.16Census Bureau. Geocoding Services Web Application Programming Interface (API)