Postal codes in South Korea

Postal codes in South Korea are composed of five digits. A new system of post codes was introduced on August 1, 2015. The first postal code in South Korea was established on July 1, 1970, and has been revised three times: in 1988, 2000, and 2015.

1970–1988
South Korea's first postal code was introduced on July 1, 1970. Individual codes were provided for each post office distribution area, using an nnn-nn numeric format (e.g., 120-01 represented Susaek-dong, Seodaemun-gu, Seoul). Unlike current postal coding provided by administrative districts, the 1970 system was implemented based upon a post office's railroad line; this often led to inconsistencies in post codes relative to their administrative areas.

Large post offices used a three-digit postal code, and small offices a five-digit code. For example, the Seoul Central Post Office's code was 100, and the Seoul Susaek-dong Post Office's was 120-01. Codes in the 700s were assigned to military posts, in the 800s to Hwanghae, the 900s to Pyongan, and the 000 range to Hamgyong.

1988–2000
Postal codes became six digits long on February 1, 1988. They were grouped by administrative areas as reflected by district reorganization and highway transportation networks. New groupings were also implemented: units in the 400s, not previously available, were allocated to Gyeonggi and Incheon, and 700s units, previously military, were changed to Gyeongbuk and Daegu. These codes utilized an nnn-nnn format; the first three digits represented, in order, the metropolitan administrative district (large city, metropolitan area, province, special autonomous area, etc.), the resident's neighborhood or ward, and a specific city, county, or district.

The last three digits matched the code to the recipient. They were assigned based on a postal carrier's delivery route. These sub-codes were divided into statutory dongs and administrative dongs, followed by myeons, and then by buildings and/or mailboxes.

2000–2015
On May 1, 2000, postal codes were assigned to each delivery agent's postal area to facilitate easier distribution. This system relied upon the codes assigned in 1988. New postal codes were subdivided to match each postman's delivery area, taking into account the introduction of automated mail sorting equipment.

Current System
The State Basic District System was introduced into South Korea on August 1, 2015. The five-digit State Basic District Number is given to each State Basic District, and it is used as a postal code of that district instead of the former six-digit code.

Assignment system
Current postal codes are structured around five digits. The first three digits represent a municipality, and the last two digits are given to the districts inside the corresponding municipality, from the northwest corner of the district to the southeast.