Area codes · +1
Area code 331
Area code 331 is centred on Aurora, Illinois. We hold 2,348 allocated blocks for it across 24 rate centres, split 44% mobile, 30% landline and 26% VoIP.
The other area codes laid over 331
Area code 331 does not have Aurora to itself. 1 other code — 630 — serves 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.
6305,043 blocks, 33 rate centres, mostly landline
Each holds its own blocks and its own carrier mix, so a 331 number and a 630 number from the same street can report different line types. Filtering Aurora by area code needs all 2 of them.
331 is not confined to Aurora itself: its blocks sit across 24 rate centres, named in the table below.
Illinois is split across 17 area codes — 224, 618, 708, 815, 217, 331 and others. By allocated blocks 331 is the 13th largest of them, holding 4% of the Illinois total.
Where 331 numbers are concentrated
NANPA truncates rate-centre names to ten characters and drops the spaces, which is why St Charles and W Chicago are shortened. Names are reproduced as recorded rather than expanded — the abbreviation is the key the block data is filed under.
| Rate centre | Blocks | Share of 331 |
|---|---|---|
| Aurora | 482 | 21% |
| Naperville | 355 | 15% |
| Downersgrv | 231 | 10% |
| St Charles | 189 | 8% |
| Lombard | 141 | 6% |
| Elmhurst | 105 | 4% |
| Lemont | 102 | 4% |
| Bartlett | 81 | 3% |
| Wheaton | 80 | 3% |
| W Chicago | 77 | 3% |
| Oswego | 71 | 3% |
| Hinsdale | 66 | 3% |
| Geneva | 62 | 3% |
| Sugargrove | 60 | 3% |
| Yorkville | 37 | 2% |
| Elburn | 31 | 1% |
| Glen Ellyn | 25 | 1% |
| Itasca | 24 | 1% |
| Plano | 22 | 1% |
| Batavia | 19 | 1% |
| Warrenvl | 18 | 1% |
| Big Rock | 17 | 1% |
| Kaneville | 13 | 1% |
| Roselle | 11 | 0% |
Carriers holding the most 331 blocks
Onvoy526 blocks
AT&T Wireless299 blocks
Verizon Wireless293 blocks
T-Mobile Usa, Inc.194 blocks
Bandwidth174 blocks
T-Mobile USA, Inc.146 blocks
The largest holder, Onvoy, has 22% of the code.
These are original allocations. A number keeps its digits and its block when its subscriber moves network, so a ported 331 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 331 number, or run a whole list through the free cleaner — neither uploads anything.
Common questions
Where is area code 331?
Area code 331 covers Aurora, Illinois. It is not the only code there: 630 is an overlay on the same rate centres, so a Aurora, Illinois number can start with any of them.
Is a 331 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 331 the split runs 44% mobile, 30% landline and 26% VoIP, so mobile is the most likely single answer.
Which carriers hold 331 numbers?
The largest holders are Onvoy, AT&T Wireless, Verizon Wireless. That is the carrier the block was allocated to, which is not necessarily the network a given number sits on today.
How many 331 numbers are there?
The code holds 2,348 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 331 covers on the order of 2,348,000 possible numbers — most of which have never been issued to anyone.