Calculated in your browser; your inputs are not sent to us. Privacy
Results update when you run the tool.
This tool processes the selected input in your browser. Review the output before relying on it; format and file behavior can vary by browser and source data.
Your inputs and results stay in this browser. This page may send privacy-bounded aggregate interaction events described in Privacy; it does not send your entered values or result contents.
Use this result
Share the current inputs or ask ChatGPT to explain the calculation in context.
More options
What does this converter do?
Enter any five digit ZIP code and the lookup returns its county, county FIPS code, central latitude and longitude, time zone, and population. For example, ZIP 00601 maps to Adjuntas municipality in Puerto Rico, FIPS code 72001, centered near 18.18004, -66.75218, with a recorded population of 18,570.
How This ZIP Code County Lookup Works
Every ZIP code in the table carries a fixed set of fields: the city name, the two letter state abbreviation, the county or county equivalent, the five digit county FIPS code, a central latitude and longitude, the IANA time zone, and the population of the area the ZIP serves. When you enter a ZIP, the tool cleans your input, formats it as a five digit code, and searches for an exact match in the reference data.
The result you see is the primary county for that ZIP. The United States Postal Service assigns each ZIP code to a default delivery area, and that area anchors to one county even when delivery routes spill across a border. For most ZIPs the primary county covers nearly every address, but rural and post office box ZIPs can be the exception, so treat the county shown as the official USPS assignment rather than a guarantee for each individual address.
Why People Look Up Counties by ZIP Code
County data shows up in more places than most people expect. Insurance carriers price homeowner and auto policies partly on county level risk, courts and record offices organize filings by county, and sales tax rules can change from one county to the next. Job applications, school enrollment forms, and government benefit paperwork often ask for a county even though most people only know their ZIP.
The FIPS code returned with the result matters for anything data related. Health agencies report statistics by county FIPS, real estate datasets key on it, and many federal forms require the numeric code instead of the county name. Because the lookup also returns latitude, longitude, time zone, and population, it doubles as a quick geographic profile for shipping zones, service area planning, or checking which time zone a customer or caller is in.
How this calculator works
Formula
This tool is a lookup, not an arithmetic calculation. It takes your five digit ZIP code and matches it against a reference table that stores the county or county equivalent, the county FIPS code, latitude, longitude, time zone, and population for each ZIP. The matching row is returned directly, so the result is one exact record rather than a computed number.
Worked example
Type 00601 into the lookup and it matches the reference row for Adjuntas: county Adjuntas, Puerto Rico, FIPS 72001, latitude 18.18004, longitude -66.75218, time zone America/Puerto_Rico, and a population of 18,570.
Assumptions to verify
- The ZIP code you enter is a valid five digit code that exists in the reference table.
- County includes county equivalents such as Louisiana parishes, Alaska boroughs, and Puerto Rico municipios.
- When a ZIP code crosses county lines, the result reports the primary county assigned to the ZIP code's default delivery area.
Frequently asked questions
How do I look up the county for a ZIP code?
Enter the five digit ZIP code in the field above and the tool returns the county or county equivalent, its FIPS code, central latitude and longitude, time zone, and population in one step.
Can a ZIP code belong to more than one county?
Yes. Some ZIP codes, especially rural routes and post office box ZIPs, span multiple counties. This lookup reports the primary county, which is the county tied to the ZIP code's default delivery area in USPS records.
What is a FIPS county code and why does it matter?
A FIPS code is a five digit Federal Information Processing Standards number that uniquely identifies a county. The first two digits are the state or territory and the last three are the county, so 72001 identifies Adjuntas in Puerto Rico. Many government forms and data systems ask for this code instead of the county name.
Cite this tool
BoringToolsKit. “ZIP Code County Lookup.” boringtoolskit.com/zip-county-lookup-calculator/. Free to reference in articles, syllabi, and answer posts with a link.
Privacy: Inputs and results stay in this browser. Any future sponsored recommendation or advertisement will be clearly labeled and kept separate from the calculation.