North American Numbers Source-cited · ownership disclosed
Area code
312
In service
United States · since 1947

Chicago (The Loop / Downtown)

One of the original 1947 area codes, 312 originally covered nearly all of the Illinois side of the Chicago metro; today it is reduced to downtown Chicago and the Loop, among the smallest area codes by geography in the nation.

The essentials Numbering data · NumberResearch · as of 2026-09-18
Place
Chicago (The Loop / Downtown)
Type
geographic
Status
in service
In service since
1947
Projected exhaust
2049 Q1

Status, dates and counts are read from NumberResearch (NANPA / CNAC / FCC records). Assignment records show initial assignees, not the carrier serving a number today.

A · Where it is

Where 312 is

Downtown Chicago - the Loop and immediate central-city environs.

Communities served wholly or partly by 312:

Chicago (downtown / Loop only)

Serves only the central downtown core; the rest of the city of Chicago is 773.

B · Relationships

How it relates to other codes

The codes 312 was split from, spawned, or shares its area with. A split divides the map and changes some numbers; an overlay shares the same ground and changes none — what's the difference?

Spawned · 1989 708 South/Near-West Chicago Suburbs Suburbs split off to new 708 on Nov 11, 1989, reducing 312 to the city of Chicago.
Spawned · 1996 773 Chicago (Outer Neighborhoods) City neighborhoods outside downtown split off to 773 in Oct 1996, leaving 312 as downtown/Loop only.
Overlay · 2009 872 Chicago (Citywide Overlay) 872 overlaid the combined 312+773 area on Nov 7, 2009.
What's changing. Overlaid by 872 (all-services overlay) since Nov 7, 2009; shares its numbering-plan area with 773.
C · History

How 312 got here

1947
Assigned as one of the original NPAs; covered almost all of the Illinois side of the Chicago metro area.
Source: Wikipedia - Area code 312
1989-11-11
Suburbs reassigned to new area code 708; 312 reduced to Chicago only.
Source: Wikipedia - Area code 312
1996-10-12
City outside downtown split off as 773; 312 reduced to downtown/Loop.
Source: Wikipedia - Area code 312
2009-11-07
Overlay 872 introduced; ten-digit dialing required.
Source: Wikipedia - Area code 312
D · Capacity

How full it is

Prefixes assigned
798
Prefixes available
2
Thousands-blocks assigned
2,576

Prefix-assignment counts describe allocation to carriers, not how many individual numbers are in use. Full technical records: NumberResearch ↗.

Compare 312 with another code →
Sources
Wikipedia ↗
Area code 312
Illinois Commerce Commission ↗
Chronological History of Area Code Relief in Illinois
NumberResearch.org ↗
Live status, dates, assignment counts and exhaust forecast — data as of 2026-09-18 (CC BY 4.0).

Place, relationships and history above are compiled by North American Numbers from the sources listed and last checked 2026-09-18. A check date is not an expert review — see how this is made. Flag an error.