O Fallon Missouri ZIP Codes

O Fallon holds 2 ZIP codes, all inside one county and one postal prefix.

We do not publish a delivery type (standard, PO box, unique) or a neighbourhood for each ZIP.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 O Fallon codes above are listed without a column we would have to invent.

Scope every ZIP code recorded for O Fallon. 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 O Fallon ZIP code begins 633. Those first three digits identify the sectional center facility that processes mail for this part of Missouri. Statewide that range covers 51 ZIP codes, so O Fallon accounts for 4% of it.

Every Missouri 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 code below serves the same ground O Fallon occupies.

• 636 Area code 636

O Fallon Missouri area codes in full →

Straight-line distance between place reference points, not driving distance. Where a place has no Census Gazetteer point, its postal centroid is used instead.