Monmouth Illinois ZIP Codes

Monmouth holds a single ZIP code.

We do not publish a delivery type (standard, PO box, unique) or a neighbourhood for each ZIP. USPS delivery-type products are licensed, and no clean-rights source maps ZIP codes to neighbourhoods — so the Monmouth codes above are listed without a column we would have to invent.

Scope every ZIP code recorded for Monmouth. Source GeoNames US postal codes (2026-07 postal dump) and Census 2024 county Gazetteer (2024 Gazetteer). Updated 15 July 2026. ZIP codes are delivery-route groupings, not areas; the boundaries implied by any ZIP map are approximations.

Every Monmouth ZIP code begins 614. Those first three digits identify the sectional center facility that processes mail for this part of Illinois. Statewide that range covers 73 ZIP codes, so Monmouth accounts for 1% of it.

Every Illinois ZIP prefix and the region it covers →

ZIP codes and area codes are separate systems — one routes mail, the other routes calls — and they do not share boundaries. The codes below serve the same ground Monmouth occupies.

• 309 Area code 309
• 861 Area code 861

Monmouth Illinois area codes in full →

Straight-line distance between place reference points, not driving distance.