331 Area Code
| State: Area Code 331 is located in the state of Illinois. | Illinois |
| Major Cities: The 3 major cities covered by Area Code 331, ordered by Census 2020 Population. | Aurora, Naperville, Bolingbrook [See All] |
| Major Counties: The 3 major counties covered by Area Code 331, ordered by Census 2020 Population. | Dupage County, Kane County, Kendall 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. | 11:45:26 AM |
| Population: The population of the 331 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. | 7,553,164 [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. | 630 |
| Parent: When the 630 Area Code began running out of available telephone numbers, Area Code 331 was created to provide relief and more telephone numbers for this geographic region. Area Code 630 is considered the parent for all of the overlays listed above. | Area Code 630 |
| 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. | 22.8% [See More] |
| Quick Link: Copy the direct link to the 331 Area Code page and use anywhere you like! |  https://www.zip-codes.com/area-code/area-code-331.asp |
Important 331 Area Code Information
Area Code 331 is located in Illinois. It covers 31 cities, including Aurora, Naperville, Bolingbrook, Wheaton, and Downers Grove. It also covers 5 counties, including Dupage County, Kane County, Kendall County, Cook County, and Will County. A full list of covered cities and counties is below including its prefix and population coverage. The 331 Area Code Map above shows the geographic region it covers.
It has a single overlay (630) that serves the same geographic area. Combined, this Area Code (and overlays), serves a population of 7,553,164.
Area Code 331 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 on Sunday, October 7, 2007. It was created as an area code overlay for the 630 Area Code.
183 Prefixes are active and currently being assigned. Of the total active prefixes, 91 (49.7%) are for Landlines, 91 (49.7%) are for Wireless numbers, and 1 (0.55%) have unknown type reservations. 621 Prefixes (77.2%) remain inactive and do not have assignments. They assigned the first prefix on Friday, July 6, 2007 and the last prefix on Friday, October 14, 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.
31 Cities covered by the 331 Area Code
| City | # Prefixes | % Prefixes | Population | % of Population |
|---|---|---|---|---|
| Aurora, IL | 93 | 31.1% | 180,542 | 2.4% |
| Naperville, IL | 97 | 32.4% | 149,540 | 2.0% |
| Bolingbrook, IL | 22 | 7.4% | 73,922 | 1.0% |
| Wheaton, IL | 32 | 10.7% | 53,970 | 0.7% |
| Downers Grove, IL | 66 | 22.1% | 50,247 | 0.7% |
| Elmhurst, IL | 48 | 16.1% | 45,786 | 0.6% |
| Lombard, IL | 44 | 14.7% | 44,476 | 0.6% |
| Bartlett, IL | 27 | 9.0% | 41,105 | 0.5% |
| Hanover Park, IL | 27 | 9.0% | 37,470 | 0.5% |
| Oswego, IL | 13 | 4.3% | 34,585 | 0.5% |
| Woodridge, IL | 66 | 22.1% | 34,158 | 0.5% |
| Saint Charles, IL | 30 | 10.0% | 33,081 | 0.4% |
| Glen Ellyn, IL | 13 | 4.3% | 28,846 | 0.4% |
| West Chicago, IL | 26 | 8.7% | 25,614 | 0.3% |
| Homer Glen, IL | 10 | 3.3% | 24,543 | 0.3% |
| Roselle, IL | 154 | 51.5% | 22,897 | 0.3% |
| Yorkville, IL | 10 | 3.3% | 21,533 | 0.3% |
| Geneva, IL | 38 | 12.7% | 21,393 | 0.3% |
| Montgomery, IL | 68 | 22.7% | 20,262 | 0.3% |
| Bensenville, IL | 124 | 41.5% | 18,813 | 0.2% |
| Lemont, IL | 30 | 10.0% | 17,629 | 0.2% |
| Hinsdale, IL | 149 | 49.8% | 17,395 | 0.2% |
| Warrenville, IL | 14 | 4.7% | 13,553 | 0.2% |
| Plano, IL | 5 | 1.7% | 11,847 | 0.2% |
| Sugar Grove, IL | 19 | 6.4% | 9,278 | 0.1% |
| Oak Brook, IL | 92 | 30.8% | 8,163 | 0.1% |
| Elburn, IL | 11 | 3.7% | 6,175 | 0.1% |
| Maple Park, IL | 3 | 1.0% | 1,433 | 0.0% |
| Big Rock, IL | 13 | 4.3% | 1,104 | 0.0% |
| Kane, IL | 2 | 0.7% | 296 | 0.0% |
| Bristol, IL | 3 | 1.0% | 0 | 0.0% |
5 Counties covered by Area Code 331
| County | # Prefixes | % Prefixes | Population | % of Population |
|---|---|---|---|---|
| Dupage, IL | 99 | 40.6% | 932,877 | 12.4% |
| Kane, IL | 72 | 29.5% | 516,522 | 6.8% |
| Kendall, IL | 50 | 20.5% | 131,869 | 1.7% |
| Cook, IL | 15 | 6.1% | 5,275,541 | 69.8% |
| Will, IL | 8 | 3.3% | 696,355 | 9.2% |
Area Code 331 Demographic Information *
| Population: The Total Population of all counties in Area Code 331 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. | 7,553,164 |
| White Population : The White Population based on Census 2020 for Area Code 331. 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. | 3,806,455 |
| Black Population : The Black Population based on Census 2020 for Area Code 331. 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. | 1,369,884 |
| Hispanic Population : The Hispanic Population based on Census 2020 for Area Code 331. 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. | 73,761 |
| Asian Population : The Asian Population based on Census 2020 for Area Code 331. 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. | 602,126 |
| Hawaiian Population : The Hawaiian or Pacific Islander Population based on Census 2020 for Area Code 331. 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. | 2,546 |
| Indian Population : The American Indian and Alaska Native population based on Census 2020 for Area Code 331. 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. | 73,761 |
| Male Population: : The Male Population from the U.S. Census for the 331 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. | 3,676,558 |
| Female Population: The Female Population from the U.S. Census for the 331 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. | 3,876,606 |
| Median Age : The Median Age for all individuals in the 331 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. | 38.00 |
| Median Age (Male) : The Median Age for all Males in the 331 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. | 37.00 |
| Median Age (Female) : The Median Age for all Females in the 331 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. | 39.20 |
| 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. | 3,114,132 |
| 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. | 2,899,073 |
| 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. | 2.57 |
| 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. | 3.28 |
* Demographic data aggregates data from all counties, based on information gathered from the 2020 Census.
Nearby Area Codes
- 224 / 847 -- Chicago, IL, Elgin, IL, Waukegan, IL
- 331 / 630 -- Aurora, IL, Naperville, IL, Bolingbrook, IL
- 464 / 708 -- Chicago, IL, Cicero, IL, Orland Park, IL
- 331 / 630 -- Chicago, IL, Aurora, IL, Naperville, IL
- 464 / 708 -- Chicago, IL, Cicero, IL, Arlington Heights, IL
- 779 / 815 -- Rockford, IL, Joliet, IL, Dekalb, IL
- 224 / 847 -- Chicago, IL, Elgin, IL, Waukegan, IL
- 773 / 872 -- Chicago, IL, Cicero, IL, Arlington Heights, IL
- 312 / 773 / 872 -- Chicago, IL, Oak Park, IL, Elmwood Park, 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 331
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 331-400-2XXX. 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
