Area Code 312

About Area Code 312

Area code 312 is a geographic telephone area code assigned to Chicago, Illinois. It operates in the Central time zone and was first introduced in 1947. Original NANP code. Chicago Loop. Overlay 872 (2009).

Within Illinois, area code 312 shares numbering capacity with 12 other area codes. The state's 12,549,689-person population (2023 Census Bureau estimate) is served by a combined 13 active codes, with 312 primarily responsible for the Chicago region. Illinois's state capital is Springfield, and its largest city is Chicago.

When you receive a call from a 312 number on your Caller ID, the call originated from a phone number assigned to the 312 area code — but be aware that Local Number Portability (in effect since 2003) means the caller could be physically located anywhere in the US or Canada. Area code 312 only confirms where the number was originally assigned.

Where is the 312 area code located?

Area code 312 is assigned to Chicago, Illinois, in the Central time zone. The state of Illinois uses 13 active area codes, and 312 is one of them. Calls placed from the 312 area code originate from numbers assigned by NANPA — the North American Numbering Plan Administrator — and the 312 prefix appears on Caller ID for both landline and wireless calls placed from this region.

The Central time zone observes Daylight Saving Time, shifting from UTC-6 to UTC-5 in summer. The local time shown above is always current, so you can quickly check whether it's a reasonable hour to call back.

What cities and counties use the 312 area code?

The 312 area code serves 11 notable cities, listed below in order of population. The largest city in the 312 territory is Chicago (2,696,555 residents in Cook County).

• Chicago, IL — 2,696,555 residents (68.7% of 312 numbers)
• Aurora, IL — 180,542 residents (4.6% of 312 numbers)
• Naperville, IL — 152,189 residents (3.9% of 312 numbers)
• Joliet, IL — 150,363 residents (3.8% of 312 numbers)
• Rockford, IL — 146,713 residents (3.7% of 312 numbers)
• Springfield, IL — 113,393 residents (2.9% of 312 numbers)
• Elgin, IL — 111,287 residents (2.8% of 312 numbers)
• Peoria, IL — 113,150 residents (2.9% of 312 numbers)
• Champaign, IL — 88,029 residents (2.2% of 312 numbers)
• Waukegan, IL — 89,321 residents (2.3% of 312 numbers)

Phone number format in area code 312

All phone numbers within area code 312 follow the standard North American 10-digit format:(312) NXX-XXXX. The NXX is the central office prefix (also called an "exchange") and XXXX is the subscriber line number. For long-distance calls within the NANP, dial 1 + 312 + NXX + XXXX. From outside North America, dial your country's international access code, then 1 (the NANP country code), then the 10-digit number.

If you need to verify whether a specific 312 number is wireless, landline, or VoIP, you can use our reverse phone lookup tool. Be aware that number portability means the area code no longer guarantees the caller's physical location — only where the number was first assigned.

History of area code 312

Original NANP code. Chicago Loop. Overlay 872 (2009).

The original 86 area codes were assigned by AT&T and Bell Labs in 1947 as part of the North American Numbering Plan. At the time, rotary-dial phones meant codes with lower digits (like 212 for NYC, 213 for LA, 312 for Chicago) were given to the largest cities because they took less time to dial. Today's area code assignments still reflect those early choices, even though touch-tone and cell phones made the original reason obsolete.

Is the 312 area code safe to answer?

Area code 312 itself is a normal geographic code with no elevated spam risk. That said, scammers can spoof any area code — including 312 — so if you don't recognize the full number, let it go to voicemail and verify the caller's identity before calling back.