Economics
FIPS Codes, ZCTAs and the Plumbing of U.S. Geographic Data
If you've ever tried to join Census data to a map and gotten lost, the problem is almost always a FIPS or ZCTA mismatch. Here's the plain-English guide.
By City Zip Compare Editorial · December 14, 2025 · 8 min read
Federal Information Processing Standards (FIPS) codes are the IDs the U.S. government assigns to geographic units. States get two-digit codes (Florida is 12, California is 06). Counties get three-digit codes within their state. ZIP Code Tabulation Areas use the five-digit ZIP.
The most common joining mistake
FIPS codes contain leading zeros. If you load them into Excel or a CSV without forcing string type, those zeros disappear and your joins silently break. Alabama becomes 1 instead of 01; Alaska becomes 2 instead of 02. Always treat FIPS as text.
ZIPs have the same problem in the Northeast — 02101 (Boston) becomes 2101.
Search any state, county, city, or ZIP without wrangling FIPS codes yourself.
Skip the Geography Headaches — Look Up a Place DirectlyState and county FIPS codes, structured
State FIPS codes run from 01 (Alabama) through 56 (Wyoming), not in alphabetical order — they were originally assigned in a mix of statehood order and administrative convenience, which is why Alabama is 01 but Alaska is 02 and Arizona is 04. County FIPS codes are three digits and are only unique within their state, so a full county identifier is the five-digit combination of state FIPS plus county FIPS (for example, 06037 is Los Angeles County, California).
How FIPS and ZCTA relate to each other
It's easy to conflate these two systems since they're both used to join Census data, but they serve different purposes and don't share a numbering scheme. FIPS codes identify governmental and administrative boundaries — states, counties, congressional districts. ZCTAs identify Census-approximated ZIP code areas, which don't align with any government boundary at all; they're purely a statistical construct built from Census block data. When you're joining Census tables to a map, know which system the table uses before attempting the join — mixing them up is the second most common source of silently broken data, right behind the leading-zero problem.
Frequently asked
›Are FIPS codes the same as ZIP codes?
No. FIPS codes identify states and counties (administrative boundaries); ZIP codes are a USPS mail-routing system, and their Census equivalent (ZCTA) is a separate, unrelated numbering approach.
›Why do state FIPS codes seem to be in a strange order?
They weren't assigned alphabetically — the sequence reflects a mix of historical statehood order and administrative decisions made when the standard was created, which is why the order looks arbitrary today.
›How do I avoid the leading-zero problem in Excel?
Format the column as text before importing the FIPS or ZIP data, or prefix the values with an apostrophe, which forces Excel to preserve them as text rather than converting them to numbers.
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Source: U.S. Census Bureau, American Community Survey 5-year estimates. Data: census.gov/programs-surveys/acs.