The area forming today’s Seodaemun-gu was first settled by humans in the Stone Age. During the Three Kingdoms Period, each of the three main kingdoms on the Korean Peninsula engaged in fierce struggles to occupy the area. During the early days of the period, it formed part of Baekje’s territory, but it was occupied by Goguryeo around 475 AD, and by Silla in 553 AD.

  The name of the area has been changed many times. It was known as Hanyang-gun during the Unified Silla Period, then as Yangju, one of the 12 administrative units (mok) under the Goryeo Dynasty. In 1396, in the early Joseon Period, Doneuimun (or Seodaemun, meaning West Gate) was built as one of the four main gates to Seoul. Thus, the area came to be called Seodaemun. King Taejo, the founder of the Joseon Dynasty, changed the name Hanyang (present-day Seoul) to Hanseong, which was composed of 52-bang grouped into 5 bu. Seodaemun belonged to Seo-bu. Present-day Seodaemun-gu extended across Bansong-bang, Banseok-bang, Sangpyeong-bang, Yeonhi-bang, and Yeongeun-bang. The area served as a hub of trade with China.

  With Japan’s annexation of Korea as its colony in 1910, part of the area came to be controlled by Goyang-gun, Gyeonggi-do. Under a new zoning system adopted in 1943, the Seodaemun Guyeokso was established within Gyeongseong-bu. Following the country’s liberation in August 1945, the name Seodaemun Guyeokso was changed to Seodaemun-gu in October 1945.

  In August 1949, Eunpyeong-myeon, Goyang-gun. Gyeonggi-do was incorporated into Seodaemun-gu, Seoul, while Daesin-dong was newly established as part of Seodaemun-gu in December 1962. Parts of Nogosan-dong and Daehyeon-dong were incorporated into Mapo-gu, while part of Ahyeon-dong, Mapo-gu was incorporated into Seodaemun-gu, in June 1964. In 1973, Gupabal-ri, Jingwannae-ri, and Jingwanoe-ri of Sindo-myeon, Gyeonggi-do were incorporated into Seodaemun-gu, while parts of Seongsan-dong and Yeonhi-dong, Seodaemun-gu were incorporated into Mapo-gu.

  Large-scale changes were made to the gu areas of Seoul in 1975. Under this reform, many areas that used to belong to Seodaemun-gu were incorporated into Jongro-gu, such as Pyeongchang-dong, Gugi-dong, Buam-dong, Hongji-dong, Sinyeong-dong, Haengchon-dong, Songwol-dong, Hongpa-dong, Pyeong-dong and parts of Gyonam-dong, Gyobuk-dong, Hyeonjeo-dong, and Chungjeong-ro 1 ga. Meanwhile, Seodomun-dong, Jeong-dong, Sunhwa-dong, Euiju-ro 2 ga and Jungrim-dong, parts of Euiju-ro 1 ga, Chungjeong-ro 1-ga, Hap-dong, Chungjeong-ro 3 ga, and Malli-dong 1/2 ga were all incorporated into Jung-gu; and Sangam-dong and Seongsan-dong and parts of Susaek-dong, Jung-dong, Namgajwa-dong, Yeonhi-dong were incorporated into Mapo-gu. Additionally, part of Malli-dong 1/2 ga was incorporated into Yongsan-gu, and part of Donggyo-dong, Mapo-gu was incorporated into Seodaemun-gu.

  The Eunpyeong-Gu Office, which was established in October 1979, incorporated the following 13 dong that used to belong to Eunpyeong Chungjangso: Nokbeon-dong, Bulgwang-dong, Galhyeon-dong, Gusan-dong, Daejo-dong, Eungam-dong, Yeokchon-dong, Sinsa-dong, Jeungsan-dong, Jingwannae-dong, Jingwanoe-dong, Gupabal-dong, and Susaek-dong.

  In 1980, Hongeun 4-dong was incorporated into Hongeun 2-dong. In 1983, part of Hongje 1-dong was incorporated into Hongje 2-dong. In 1989, part of Daehyeon-dong was incorporated into Bukahyeon 3-dong and part of Bukahyeon 3-dong into Chungjeong-ro 3 ga. In 1998, Hyeonjeo-dong was incorporated into Cheonyeon-dong.