ZIP to State

Finding the state for a US ZIP code is one of the most fundamental postal data operations — critical for address form auto-fill, sales tax calculation, shipping rate determination, regulatory compliance, and data validation across virtually every industry that handles US addresses. Our ZIP to State tool returns the two-letter USPS state abbreviation and full state name for any 5-digit US ZIP code in milliseconds, covering all 50 states, Washington DC, and all inhabited US territories.

How ZIP Codes Are Organized by State

The first digit of a US ZIP code identifies a broad national delivery region, and the first three digits together identify a Sectional Center Facility (SCF) — a regional mail processing hub that handles all mail entering and leaving a multi-ZIP area. Because SCFs are built to serve geographic regions that often align with state boundaries, ZIP codes tend to cluster within specific numeric ranges by state.

The 0xxxx range covers northeastern states: Connecticut (060–069), Maine (039–049), Massachusetts (010–027), New Hampshire (030–038), New Jersey (070–089), Rhode Island (028–029), Vermont (050–059), and parts of New York (100–149), plus Puerto Rico (006–009) and the US Virgin Islands (008). The 1xxxx–2xxxx range covers Mid-Atlantic states including New York (100–149), Pennsylvania (150–196), Delaware (197–199), Maryland (206–219), Virginia (220–246), West Virginia (247–268), and North Carolina (270–289). The 3xxxx range covers the Southeast: South Carolina (290–299), Georgia (300–319), Florida (320–349), Alabama (350–369), Tennessee (370–385), Mississippi (386–397). The 4xxxx range covers the Great Lakes states: Kentucky (400–427), Indiana (460–479), Michigan (480–499), Ohio (430–458). The 5xxxx range covers the Upper Midwest: Iowa (500–528), Minnesota (550–567), Wisconsin (530–549), South Dakota (570–577), North Dakota (580–588), Nebraska (680–693). The 6xxxx–7xxxx range covers South-Central states: Illinois (600–629), Missouri (630–658), Kansas (660–679), Arkansas (716–729), Oklahoma (730–749), Texas (750–799), Louisiana (700–714). The 8xxxx range covers the Mountain West: Colorado (800–816), Wyoming (820–831), Utah (840–847), Arizona (850–865), New Mexico (870–884), Nevada (889–898), Idaho (832–839), Montana (590–599). The 9xxxx range covers the Pacific region: California (900–961), Oregon (970–979), Washington (980–994), Alaska (995–999), Hawaii (967–968), and Pacific territories.

Why You Cannot Reliably Determine State from the First Digit Alone

While the first digit gives a regional clue, numerous exceptions prevent reliable single-digit state lookup. Puerto Rico (00600–00988) shares the 0 prefix with New England states. Military overseas mail (APO AE 090–098, APO AP 962–966, APO AA 340) uses ranges that overlap with civilian US ZIPs. And a small number of ZIP codes near state borders have been assigned to a neighboring state SCF for logistical efficiency, meaning their first digits suggest one state but their actual state is different. Always use a full ZIP database lookup for accurate state determination.

ZIP to State for Form Validation and Auto-Fill

The most widespread web development use of ZIP-to-state conversion is populating the state field automatically when a user enters their ZIP code. This reduces checkout friction, prevents state field typos, and ensures database consistency. Beyond the user experience benefit, auto-populated state data is more reliable than user-typed state names because users frequently abbreviate, misspell, or select the wrong option from a dropdown.

For a robust implementation: fire the ZIP lookup after the 5th character is entered, return state abbreviation and full name in the response, update both the state field value and any hidden state_code input, and mark the field as programmatically set so your front-end validation layer knows not to re-flag it as empty. Allow user override — some edge-case ZIP codes genuinely serve addresses in two states.

ZIP to State for Tax Calculation

Sales tax in the United States is state-administered, and rates vary dramatically: from 0% in states with no sales tax (Oregon, Montana, New Hampshire, Delaware, Alaska at the state level) to over 10% when state plus local rates are combined in places like Louisiana, Tennessee, and Arkansas. Determining the correct state from the billing ZIP is the first step in any sales tax calculation workflow. After resolving the state, a tax service such as TaxJar, Avalara, or the Vertex platform applies the combined state + county + city + special district rate for the exact delivery address.

Compliance and Regulatory Use Cases

Many regulated industries have state-specific restrictions. Insurance products are licensed by state. Financial products are regulated at the state level. Healthcare marketing must comply with state-specific patient privacy laws that go beyond federal HIPAA minimums. In all these cases, the ZIP-to-state resolution is the first step in the compliance chain: identify the state, then apply the rule set for that state. ZIP codes that span two states (extremely rare, fewer than 20 documented cases nationally) require special handling — our tool flags these and returns both states.

Storing ZIP Codes: VARCHAR vs INT

A recurring data quality issue is the loss of leading zeros in ZIP codes stored as integers. ZIP code 02134 (Boston, MA) stored as an integer becomes 2134 — a ZIP that does not exist and fails all lookups. This error cascades: ZIP-to-state lookups return null, address validation fails, form auto-fill breaks, and records become unsegmentable by state. The fix is simple but requires discipline: always declare ZIP code columns as VARCHAR(5) or TEXT in databases, and format ZIP cells as Text in spreadsheets before entering data. In JavaScript, treat ZIP codes as strings from the moment they arrive — never run parseInt() on a ZIP code.

Historical ZIP Code Geography and State Assignments

USPS SCF boundaries were drawn in the early 1960s for operational efficiency, not to mirror state political boundaries precisely. Over 60 years, population shifts and postal route reorganizations have caused a small number of ZIP codes to be reassigned across SCFs — but the state-level assignment for the vast majority of ZIP codes has remained stable. The approximately 42,074 active US ZIP codes cover every inhabited corner of the continental US, Alaska, Hawaii, and US territories, with state assignments that reflect current USPS operational regions.