Area codes in Montclair, California
Montclair, California uses 2 area codes — 909 and 840. The main Montclair area code is 909.
Area codes serving Montclair
Phone numbers in Montclair are written as ten digits — for example (909) 555-0190 — and fall in the Pacific Time zone.
How Montclair came to have 2 area codes
The original Montclair area code is 909, in service since 1992. As the area ran low on available numbers, an overlay code was added over the same region for new phone lines: 840 (2021). Existing numbers kept their original code — an overlay never forces anyone to change their number — which is why Montclair now uses all 2 codes and every local call is dialed with ten digits.
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Frequently asked questions
What is the area code for Montclair?
The main area code for Montclair, California is 909. Montclair is now served by 2 area codes in total: 909, 840.
How many area codes does Montclair have?
Montclair has 2 area codes: 909, 840.
Why does Montclair have more than one area code?
As Montclair used up the numbers available in its original area code (909, in service since 1992), additional "overlay" codes were added over the same area so new phone numbers could keep being assigned.
How do you dial a Montclair number?
Dial all 10 digits — the area code (909 or 840) followed by the 7-digit local number. From abroad, dial +1, then the area code and number.
Sourced from the official NANPA (North American Numbering Plan Administrator) numbering database, current as of August 2, 2026. Refreshed monthly.