Postal codes in South Korea

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 Search Post 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.

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.

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 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.