Yeosu, formerly romanized as Yosu, is a coastal city located on the southern shore of South Korea. With a population of 268,823, Yeosu is the second largest city in South Jeolla Province. In 1998, the Old Yeosu City, Yeocheon City and Yeocheon County were merged and the current city, Yeosu, was formed.

The place name "Yeosu" first appears in the Samguk Sagi Jiriji with the record: "Haeeup-hyeon (海邑縣) was originally Baekje's Wonzon-hyeon (猿村縣), but King Gyeongdeok changed its name. It is now Yeosu-hyeon (麗水縣) in Goryeo." In both Dongramdo(part of Donggukyeojiseungram)and Dongyeobigo (Jeollado's part), the name "Suyoung" (水營) is noted on the southern peninsula south of Suncheon and Gwangyang. This is believed to be because Jeollado's Jwasuyoung (Joseon Dynasty's Naval Headquarters for eastern sector of Jeolla Province) was established in this region starting in 1479 (the 10th year of King Seongjong's reign). Subsequently, most old maps depict it as "Yeosu" (呂水), written differently from the current Hanja. Specifically, in the Haedongdo (Suncheon) map, Jwasuyoung appears south of Yeosumyeon (呂水面).

The Neolithic sites in Yeosu were excavated and investigated by the National Gwangju Museum from 1989 to 1990. The artifacts unearthed include various types of pottery such as Yunggimong pottery, Apinmung pottery, Chimsunmung pottery, Jeomnyeolmung pottery, Juchil pottery, and Mummun pottery, as well as stone tools including milgae (hammerstones), jjikkgae (flint tools), jargegae (sickles), geukkeogae (scraping tools), saegigae (engraving tools), doggi (axes), galdol (grinding stones), and suttol (whetstones). Additionally, two residential sites were investigated.

The residential sites were constructed by compacting clay over shell layers, with diameters ranging from 460 to 540 centimeters, and featured a circular, flat layout equipped with round kilns. Notably, at the first residential site, a set of tools including a moru-dol (grindstone), galpan (grinding plate), and another galdol (grinding stone) were found near the kiln area. These tools allowed for the crushing or grinding of materials to produce powder, which drew significant attention. The radiocarbon dating of the Songdo shell mound indicated an age of 4285±195 BP and 4270±200 B.C.

In 1992 and 1993, surface surveys were conducted in the islands of Yeosu, leading to the additional investigation of 22 Neolithic shell mounds and 3 artifact dispersal sites. This revealed that the island regions of Yeosu, along with the coastal areas of South Gyeongsang Province, were cultural centers of the Neolithic period. The site locations were predominantly situated in bays suitable for various shellfish habitats, being safe from sea winds and featuring well-developed shell pits. The collected artifacts were similar to those unearthed from the Songdo shell mound, and a considerable number of Yunggimong pottery, which is dated to a relatively early period, were excavated.

In the Yeosu region during the Proto Three Kingdoms Period period, there appears to have been Wonji-guk (爰池國), one of the Mahan confederations. However, in the late 4th century, as Baekje expanded its power, several small states located in the present-day Jeollanam-do region came under Baekje's influence. Baekje did not immediately reorganize these small states into counties (郡縣) or dispatch local governors. Instead, Baekje recognized the authority of the chieftains of these small states and exercised indirect control through them by collecting tributes. It is believed that the Yeosu region was incorporated into Baekje under such circumstances.

In the mid-5th century, Baekje's national power was significantly weakened due to Goguryeo's southward expansion. Additionally, as the Gaya Kingdom advanced into the lower regions of the Namyun and Seomjin rivers, the eastern part of Jeollanam-do was temporarily incorporated into Daegaya (Great Gaya). In 538, Baekje moved its capital to Sabi-seong and divided the entire country into five regions (五方) centered around the central, eastern, western, southern, and northern areas. In each region, Baekje established Bangseong (方城) and governed through these large and small fortresses, managing them as counties (郡) or prefectures (縣). In the southern region, now corresponding to Suncheon, Yeosu, and Gwangyang areas, Sapyeong-gun (歃平郡) was established.

Within Sapyeong-gun, there were three counties: Wonzon (猿村), Maro (馬老), and Dolsan (突山). Wonzon-hyeon (猿村縣) covered the Yeosu Peninsula, while Dolsan-hyeon (突山縣) included Dolsan-do and nearby islands. From this time, the Yeosu region saw the first establishment of counties named Wonzon and Dolsan.