ZIP Code 01821 – Billerica, Massachusetts

ZIP Code 01821 for Billerica, Massachusetts is part of the United States postal code system, which uses a numeric code of 5 (or 5+4) digits (e.g. 10001). Addresses here are organised as State → County → City. Within the code structure it maps to ZIP Code 01821.

Administratively it is recorded in Middlesex, Massachusetts within United States. Postal codes are assigned by delivery route rather than by administrative boundary, so a single code can cover more than one locality and a locality can fall under several codes.

No building-level records are held for this code in the imported dataset, so only the code and its location details are shown. The absence of records does not mean the zip code is unused.

Couriers, e-commerce checkout forms and address autocomplete tools all rely on the zip code to route mail and to check that a stated address matches the code. Because a zip code identifies a delivery area rather than a single building, two addresses that share the same code can still be some distance apart.

Always write United States ZIP Code in full when completing a form, including any leading zero. Enter a valid US ZIP Code, e.g. 10001 or 10001-1234. Data source: a third-party open dataset. This is a reference snapshot, not a live government feed, so confirm the code with the sender, carrier or postal authority before relying on it.