North American Numbers Source-cited · ownership disclosed
Area code
815
In service
United States · since 1947

Northern Illinois (Rockford)

One of the original 1947 area codes, 815 covers most of northern Illinois outside the Chicago metro core and outside the Quad Cities. It was split once (creating 309 in 1957) and has been overlaid by 779 since 2007.

The essentials Numbering data · NumberResearch · as of 2026-09-18
Place
Northern Illinois (Rockford)
Type
geographic
Status
in service
In service since
1947
Projected exhaust
2044 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 815 is

Northern Illinois excluding the Chicago core - north-central and north-western Illinois, plus Joliet; excludes the Illinois Quad Cities.

Communities served wholly or partly by 815:

RockfordJolietDeKalbLaSalleOttawaFreeportSterlingKankakeeCrystal Lake

Representative subset; the region spans many counties across northern Illinois.

B · Relationships

How it relates to other codes

The codes 815 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 · 1957 309 West-Central Illinois (Peoria) Western portion of 815 combined with part of 217 to create 309 in 1957.
Overlay · 2007 779 Northern Illinois (overlay of 815) 779 added as an all-services overlay over the entire 815 geography in 2007.
What's changing. Overlaid by 779 since March 2007; ten-digit dialing mandatory across the 815/779 area.
C · History

How 815 got here

1947
Established as one of the original NANP area codes, assigned to the northern band of Illinois outside Chicago.
Source: Wikipedia - Area code 815
1957
815 split; western portion combined with part of 217 to form area code 309.
Source: Wikipedia - Area code 815
2007-02-17
Ten-digit dialing began across the 815 area in preparation for the 779 overlay.
Source: Wikipedia - Area codes 815 and 779
2007-03-17
Overlay code 779 activated over the same geography.
Source: Wikipedia - Area codes 815 and 779
D · Capacity

How full it is

Prefixes assigned
800
Prefixes available
0
Thousands-blocks assigned
3,121

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

Compare 815 with another code →
Sources
Wikipedia ↗
Area code 815
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.