Area codes · +1
Area code 312
Area code 312 covers Chicago. We hold 4,675 allocated blocks for it across 8 rate centres, split 36% mobile, 57% landline and 8% VoIP.
The other area codes laid over 312
Area code 312 does not have Chicago to itself. 2 other codes — 773, 872 — serve the same rate centres, laid over the same ground rather than dividing it. That is an overlay: a new code added when the old one ran out of numbers, covering the same streets. Two neighbours can hold different area codes, so the code says roughly when a number was issued rather than where it sits.
Each holds its own blocks and its own carrier mix, so a 312 number and a 773 number from the same street can report different line types. Filtering Chicago by area code needs all 3 of them.
312 is not confined to Chicago itself: its blocks sit across 8 rate centres, named in the table below.
Illinois is split across 17 area codes — 224, 618, 708, 815, 217, 312 and others. By allocated blocks 312 is the 10th largest of them, holding 7% of the Illinois total.
Where 312 numbers are concentrated
Rate-centre names are reproduced as NANPA records them. The agency truncates them to ten characters, so longer names appear shortened elsewhere on this site.
| Rate centre | Blocks | Share of 312 |
|---|---|---|
| Chicago | 4,546 | 97% |
| Wheeling | 35 | 1% |
| Northbrook | 22 | 0% |
| Hinsdale | 20 | 0% |
| La Grange | 18 | 0% |
| Chicago | 11 | 0% |
| Chicago | 11 | 0% |
| Roselle | 4 | 0% |
Carriers holding the most 312 blocks
Illinois Bell1,124 blocks
T-Mobile Usa, Inc.528 blocks
T-Mobile USA, Inc.395 blocks
AT&T Wireless367 blocks
Bandwidth286 blocks
Onvoy262 blocks
The largest holder, Illinois Bell, has 24% of the code.
These are original allocations. A number keeps its digits and its block when its subscriber moves network, so a ported 312 number still reports the carrier it started with. Closing that gap needs a live query against the routing database. How line type is derived.
Check a single 312 number, or run a whole list through the free cleaner — neither uploads anything.
Common questions
Where is area code 312?
Area code 312 covers Chicago. It is not the only code there: 773, 872 are overlays on the same rate centres, so a Chicago number can start with any of them.
Is a 312 number a mobile or a landline?
It can be either, and the digits do not say which. North American mobile and landline numbers share the same ranges, so the answer comes from the carrier holding the block. In 312 the split runs 36% mobile, 57% landline and 8% VoIP, so landline is the most likely single answer.
Which carriers hold 312 numbers?
The largest holders are Illinois Bell, T-Mobile Usa, Inc., T-Mobile USA, Inc.. That is the carrier the block was allocated to, which is not necessarily the network a given number sits on today.
How many 312 numbers are there?
The code holds 4,675 allocated blocks in our copy of the numbering plan. A block is 1,000 or 10,000 consecutive numbers depending on how deeply it has been pooled, so 312 covers on the order of 4,675,000 possible numbers — most of which have never been issued to anyone.