Area codes / Illinois / 331
The 331 area code
331 is an area code in Illinois, in the Central time zone. Get a local 331 number for your business, shared by everyone who answers it, or bring the 331 number you already have.
331 at a glance
Get a 331 business number
When you sign up for Onyx Phone, you pick a local number by area code: search 331, narrow it by the next three digits or the last four if you want something memorable, and it's yours on the spot. Which numbers are free changes daily. If you don't find one you like, 630 covers the same area.
The number rings everyone you assign to it, in the browser, on the iPhone and Android apps, and on desk phones, and texts from it are unlimited once US carriers approve your business. Your plan includes one number for each user, and more numbers are $5 a month.
Calling 331 customers
Local calls within 331 can be dialed with seven digits. Callers are on Central time, so set your business hours to match if most of your customers are here.
Calls from Onyx Phone show your business number, and once your business is verified, your caller ID name too, so 331 customers see who's calling.
Questions about area code 331
What state is area code 331?
Area code 331 is in Illinois.
What time zone is area code 331 in?
Area code 331 is in the Central time zone.
Is 331 an overlay area code?
Yes. 331 shares its area with 630. Numbers in either code ring the same region, and local calls there are dialed with all ten digits.
Can I get a 331 business number?
Onyx Phone sells US local numbers. When you pick your number, search the 331 area code; which numbers are free changes daily. If none are free, 630 covers the same area.
Can I keep the 331 number I already have?
Yes. Moving a number to Onyx Phone is free on every plan and usually takes 3 to 7 business days. You answer on a temporary number until it moves.
Included on every plan
Starter is $17, Business is $29, Scale is $42 per user a month, or less billed yearly. The plan includes a business number for each user and unlimited calling and texting in the US and Canada. Every plan starts with a 7-day free trial, and moving your current number over is free.
Area code data from the North American Numbering Plan Administrator (NANPA), file of October 24, 2026.