Area codes in Rialto, California
Rialto, California uses 2 area codes — 909 and 840. The main Rialto area code is 909.
Area codes serving Rialto
Phone numbers in Rialto are written as ten digits — for example (909) 555-0190 — and fall in the Pacific Time zone.
How Rialto came to have 2 area codes
The original Rialto 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 Rialto 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 Rialto?
The main area code for Rialto, California is 909. Rialto is now served by 2 area codes in total: 909, 840.
How many area codes does Rialto have?
Rialto has 2 area codes: 909, 840.
Why does Rialto have more than one area code?
As Rialto 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 Rialto 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.