Diamond Bar California Area Codes

2 area codes cover Diamond Bar: 840 and 909. A number carrying any of them is local to Diamond Bar.

A code in the “shares ground” column is an overlay: it covers the same territory rather than a different part of Diamond Bar, which is why local calls there are dialled as ten digits.

Scope the codes matched to Diamond Bar. Source geoinfo-dataset (full_dataset) ZIP→NPA (2018 snapshot) and LocalCallingGuide NPA list (2026-07 NPA list). Updated 16 July 2026. Overlay relationships come from the numbering-plan authority; the place match is computed.

We do not publish which of these codes covers which street or neighbourhood in Diamond Bar, and we would rather say so than guess. Area codes are drawn around telephone rate centres, which follow neither municipal boundaries nor ZIP codes, and the per-ZIP telephone data we hold is a 2018 snapshot too noisy to split a city with. Where these codes overlay one another the question has no answer at all: they cover the same ground by design. Awaiting a current, clean-rights rate-centre boundary source.

Postal geography is organised separately from telephone geography, so Diamond Bar’s 1 ZIP code do not map onto the codes above. They are listed in full, with the county each falls in, on the postal side of the site.

Diamond Bar California ZIP codes →

These are the closest places to Diamond Bar whose area codes are not the same set. If you are near one of them, a local number may carry a code that is not on the list above.

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