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Illinois (IL)Central Time (CT)

Area Code 312

Illinois (IL) * Chicago * Central Time (CT)

300.9K

Population

13

ZIP codes

Illinois

Primary state

Central Time (CT)

Time zones

What stands out

  • Coverage: 300.9K people across 13 ZIP codes (primarily Cook County, IL).
  • Overlapping area codes: 872
  • Major cities: Chicago.
Primary state:Illinois (IL)/Major cities:Chicago

Browse sections

Basics

Percentiles compare this area code to other area codes nationwide.

Population

300.9K

ZIP codes

13

Median age

33.9 yrs

Population density

20.2K/sq mi

Mean commute time

26 min

Avg. household size

1.7

Neighbors

Neighboring area codes

773872
Notes & Sources
  • Area-code boundaries can change over time; verify official assignments with NANPA for critical use.
  • In regions with overlapping area codes, new numbers may use a different code.
  • This page aggregates ZIP-based crosswalks for orientation and does not indicate phone-number availability.

Data freshness

ACS 5-year
2020–2024
Page updated
2026-02-23

Release schedule and upstream dates: Sources.

Data sources

U.S. Census (ACS 5-year)U.S. Census TIGER/LineNANPA

Derived statistics

  • Area codes are not Census geographies; statistics are estimated by aggregating ZCTA (ZIP) values for associated ZIPs.
  • ZIP↔area code associations are derived from NPA boundary polygons and ZCTA centroid points, and can be approximate.
  • Median age, mean commute, and household size are population-weighted; population density uses summed ZIP land area.
Area code overlays and service areas are primarily governed by NANPA; this page uses aggregated geographic overlays for orientation only.

Data accuracy & methodology

This report aggregates 2020–2024 ACS 5-year estimates and geographic overlays for orientation. Area code service areas can cross ZIP/state boundaries and change over time; verify official assignments with NANPA for critical use.