Data Last Updated: April 1, 2024

312 Area Code

State: Area Code 312 is located in the state of Illinois.	Illinois
Major Cities: The 3 major cities covered by Area Code 312, ordered by Census 2020 Population.	Chicago, Cicero, Schaumburg [See All]
Major Counties: The 3 major counties covered by Area Code 312, ordered by Census 2020 Population.	Cook County, Lake County, Dupage County [See All]
Timezone(s): The Time Zone(s) covered. Multiple time zones can be covered. Please note that not all parts of the U.S. observe daylight saving time which can affect actual local time for this area. There are 7 standard time zones which are, from west to east: Hawaii-Aleutian, Alaska, Pacific, Mountain, Central, Eastern, Atlantic. Also included in U.S. Territories are Samoa, Guam and Palau.	Central (GMT -06:00)
Local Time: The current local time for each timezone. If more than 1 time zone for this area, all local times will be shown. Keep in mind that area codes can cross timezones, so more than 1 may be shown.	11:43:20 AM
Population: The population of the 312 Area Code is calculated by adding the population of all counties covered from the U.S. Census 2020. Included are U.S. Citizens, permanent residents, temporary migrants, and undocumented individuals. The total population represents people who live here, not just those present while the Census was being completed.	6,922,760 [See All]
Overlays: An area code overlay happens when multiple codes cover the same geographic region. This is done by introducing a new area code to the same region as the existing one that needs assistance and more telephone numbers. In this situation, existing customers retain their current area code and phone number while a new code provides more telephone numbers.	872
Prefix Assignment: There are 800 possible prefixes per Area Code. This shows how much of those prefixes have been assigned to a telcom company. A high percentage of assignment shows that numbers are running out and close to being exhausted. When this occurs, Overlays are created to increase how many numbers are available for this geographic area. A geographic region can also be "split" into smaller geographic regions. One region retains the existing area code with a new code created for the other region.	97.4% [See More]
Quick Link: Copy the direct link to the 312 Area Code page and use anywhere you like!	https://www.zip-codes.com/area-code/area-code-312.asp

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Important 312 Area Code Information

Area Code 312 is located in Illinois. It covers 16 cities, including Chicago, Cicero, Schaumburg, Glenview, and Buffalo Grove. It also covers 3 counties, including Cook County, Lake County, Dupage County. A full list of covered cities and counties is below including its prefix and population coverage. The 312 Area Code Map above shows the geographic region it covers.

It has a single overlay (872) that serves the same geographic area. Combined, this Area Code (and overlays), serves a population of 6,922,760.

Area Code 312 has a single Timezone of Central (GMT -06:00). The table above displays the current local time for each time zone. Please remember that while the majority of this region may observe Daylight Saving Time, small localized areas may not. Our ZIP Code Database shows which ZIP Codes observe DST.

NANPA (North American Numbering Plan Administrator) put this area code into service prior to January, 1, 1947 (when data tracking began)

On Friday, July 23, 1999, NANPA announced Area Code 872 is an overlay relief and put it into service on Saturday, November 7, 2009.

779 Prefixes are active and currently being assigned. Of the total active prefixes, 505 (64.8%) are for Landlines, 273 (35.0%) are for Wireless numbers, and 1 (0.13%) have unknown type reservations. 21 Prefixes (2.6%) remain inactive and do not have assignments. They assigned the first prefix on Friday, February 4, 1994 and the last prefix on Monday, September 19, 2022.

This Area Code is not in jeopardy, so it will not run out of numbers before a change can be made. No relief planning is currently underway.

16 Cities covered by the 312 Area Code

City	# Prefixes	% Prefixes	Population	% of Population
Chicago, IL	1,808	211.7%	2,746,388	39.7%
Cicero, IL	19	2.2%	85,268	1.2%
Schaumburg, IL	179	21.0%	78,723	1.1%
Glenview, IL	167	19.6%	48,705	0.7%
Buffalo Grove, IL	48	5.6%	43,212	0.6%
Wheeling, IL	62	7.3%	39,137	0.6%
Northbrook, IL	238	27.9%	35,222	0.5%
Roselle, IL	154	18.0%	22,897	0.3%
Brookfield, IL	168	19.7%	19,476	0.3%
Deerfield, IL	177	20.7%	19,196	0.3%
Hinsdale, IL	149	17.4%	17,395	0.3%
Prospect Heights, IL	32	3.7%	16,058	0.2%
Western Springs, IL	215	25.2%	13,629	0.2%
La Grange Park, IL	172	20.1%	13,475	0.2%
Clarendon Hills, IL	44	5.2%	8,702	0.1%
Medinah, IL	97	11.4%	0	0.0%

3 Counties covered by Area Code 312

County	# Prefixes	% Prefixes	Population	% of Population
Cook, IL	783	96.7%	5,275,541	76.2%
Lake, IL	14	1.7%	714,342	10.3%
Dupage, IL	13	1.6%	932,877	13.5%

Area Code 312 Demographic Information *

Population: The Total Population of all counties in Area Code 312 from the U.S. Census. This reflects the exact population of the city at the time the Census was completed, not an estimate. It includes all people regardless of their citizenship or immigration status.	6,922,760
White Population : The White Population based on Census 2020 for Area Code 312. On the 2020 U.S. Census questionnaire, people were asked to check all races which applied to them, including White. This count includes all who selected White/Caucasian in their response, even if they selected another race as well.	3,398,208
Black Population : The Black Population based on Census 2020 for Area Code 312. On the 2020 U.S. Census questionnaire, people were asked to check all races which applied to them, including Black or African American. This count includes all who selected Black or African American in their response, even if they selected another race as well.	1,300,375
Hispanic Population : The Hispanic Population based on Census 2020 for Area Code 312. On the 2020 U.S. Census questionnaire, people were first asked for their Ethnicity, including if they were from Hispanic, Latino, or Spanish Origin, including Mexican, Mexican American, Chicano, Puerto Rican, Cuban, or other ethnic origin. This count includes all who affirmed that they were part of this ethnic origin. Respondants were also asked to select their race from the options above as well. Hispanic is not a racial designation, it is an Ethnic designation.	69,160
Asian Population : The Asian Population based on Census 2020 for Area Code 312. On the U.S. Census questionnaire, people were asked to check all races which applied to them, including Chinese, Filipino, Asian Indian, Vietnamese, Korean, Japanese, or Other Asian. This count includes all who selected one of these options in their response, even if they selected another race as well.	592,333
Hawaiian Population : The Hawaiian or Pacific Islander Population based on Census 2020 for Area Code 312. On the 2020 U.S. Census questionnaire, people were asked to check all races which applied to them, including Native Hawaiian and Pacific Islander. This count includes all who selected either Hawaiian or Pacific Islander in their response, even if they selected another race as well.	2,619
Indian Population : The American Indian and Alaska Native population based on Census 2020 for Area Code 312. On the 2020 U.S. Census questionnaire, people were asked to check all races which applied to them, including American Indian and Alaska Native. This count includes all who selected American Indian and Alaska Native in their response, even if they selected another race as well.	69,160
Male Population: : The Male Population from the U.S. Census for the 312 Area. The population numbers are not projected to the future, they are actual Census 2020 counts. Each respondent self-identified their gender on the survey, as they were asked to indicate their gender assigned at birth.	3,367,158
Female Population: The Female Population from the U.S. Census for the 312 Area. The population numbers are not projected to the future, they are actual Census 2020 counts. Each respondent self-identified their gender on the survey, as they were asked to indicate their gender assigned at birth.	3,555,602
Median Age : The Median Age for all individuals in the 312 Numbering plan area. The median age numbers are not projected to the future, they are actual Census 2020 numbers. The median age is the age at the midpoint of the population. Half of the population is older than the median age and half of the population is younger.	38.67
Median Age (Male) : The Median Age for all Males in the 312 Numbering plan area. The median age is the age at the midpoint of the population. Half of the population is older than the median age and half of the population is younger. Gender is self reported by individuals when asked for their gender at birth.	37.67
Median Age (Female) : The Median Age for all Females in the 312 Numbering plan area. The median age is the age at the midpoint of the population. Half of the population is older than the median age and half of the population is younger. Gender is self reported by individuals when asked for their gender at birth.	40.33
Total Housing Units: The total number of Housing Units is the number of occupied units + the number of vacant units. Ownership is defined by whether the unit is occupied by an owner or by a tenant. Owner occupancy means that the owner lives in the unit. This value comes from the 2020 U.S. Census and is not a projection or estimate.	2,899,314
Total Households : Total Number of Households from the 2020 U.S. Census for this geographic area. A Household includes everyone living in a residential housing unit. This includes families, roommates in a single residence, or a person living alone.	2,688,542
Average Household Size : The Average Household Size, is obtained by dividing the number of people in Households (excluding those in group quarters, nursing home, prisons, and dorm rooms) by the number of Households. A Household includes everyone living in a residential unit. Those who do not live in a household are classified as living in group accommodation. This value is an estimate from the U.S. Census ACS (American Community Survey) and is updated yearly.	2.53
Average Family Size : Average Family Size is calculated by dividing the number of people in a Family Household by the number of Family Households. The U.S. Census Bureau defines family households as households consisting of two or more individuals who are related by birth, marriage, or adoption. They also may include other unrelated people. Non-family households consist of people who live alone or who share their residence with unrelated individuals. The Average Family Size only looks at the households classified as Family Households. This value is an estimate from the U.S. Census ACS (American Community Survey) and is updated yearly.	3.32

* Demographic data aggregates data from all counties, based on information gathered from the 2020 Census.

Nearby Area Codes

312 / 872 -- Chicago, IL, Cicero, IL, Schaumburg, IL
773 / 872 -- Chicago, IL, Cicero, IL, Arlington Heights, IL
312 / 773 / 872 -- Chicago, IL, Oak Park, IL, Elmwood Park, IL
464 / 708 -- Chicago, IL, Cicero, IL, Orland Park, IL
224 / 847 -- Chicago, IL, Elgin, IL, Waukegan, IL
219 -- Hammond, IN, Gary, IN, Portage, IN
331 / 630 -- Aurora, IL, Naperville, IL, Bolingbrook, IL

All Area Codes and areas served in the state of Illinois

217 -- Chicago, IL, Springfield, IL, Champaign, IL
224 -- Chicago, IL, Elgin, IL, Waukegan, IL
309 -- Peoria, IL, Bloomington, IL, Normal, IL
312 -- Chicago, IL, Cicero, IL, Schaumburg, IL
331 -- Aurora, IL, Naperville, IL, Bolingbrook, IL
447 -- Springfield, IL, Champaign, IL, Decatur, IL
464 -- Chicago, IL, Cicero, IL, Orland Park, IL
618 -- Belleville, IL, Granite City, IL, Alton, IL
630 -- Chicago, IL, Aurora, IL, Naperville, IL
708 -- Chicago, IL, Cicero, IL, Arlington Heights, IL
773 -- Chicago, IL, Cicero, IL, Arlington Heights, IL
779 -- Rockford, IL, Joliet, IL, Dekalb, IL
815 -- Chicago, IL, Rockford, IL, Joliet, IL
847 -- Chicago, IL, Elgin, IL, Waukegan, IL
861 -- Peoria, IL
872 -- Chicago, IL, Oak Park, IL, Elmwood Park, IL

Prefix Assignment & Usage for 312

Prefix Assignment

Usage Type

Assignment shows how many of the 800 Prefixes (NXXs) possible have been assigned to a telcom provider. Once assigned, that provider can start issuing numbers for that prefix. Only Prefixes from 200-999 are possible.

A high percentage of assignments indicate that the number availability in this area is exhausting and may soon run out. Overlays and Splits will add more number options to alleviate the shortage of the parent area code.

A Split can also happen where the geographic region is split into two smaller parts. While a new code is made to cover a different region, one area code remains unchanged.

Usage shows how the prefixes are designated for use by the telcom provider, either landline or wireless. Telcoms can sub-license out parts of the prefixes to other carriers who may use it for any purpose needed. For example, a carrier might license the 2000 block of 312-400-2XXX. Even if the 400 Prefix is designated as landline, they can use these numbers for wireless use.

Number Portability from the Telecommunications Act of 1996 has also made it so individuals can take a landline number and move to a wireless carrier (and vice versus). While Usage data is still helpful, its utility is fading with "cord cutting" and the shift from landline to wireless use.

References

North American Numbering Plan Administrator: NANPA [Updated Quarterly], https://nationalnanpa.com
ZIP-Codes.com Internal Data Creation [Last Updated: 9/1/2023], https://www.zip-codes.com
U.S. Census 2020 [Decennial] [Last Updated: 5/25/2023], https://www.census.gov