The Jin state was an early Korean Iron Age state which occupied some portion of the southern Korean peninsula during the 2nd and 3rd centuries BC, bordering the Korean kingdom Gojoseon to the north. Its capital was somewhere south of the Han River. It preceded the Samhan confederacies, each of which claimed to be successors of the Jin state.
It is not clear as to how well defined of an organized state Jin was. It seems likely that it was a federation of small states much like the subsequent Samhan. For the state to be able to contend with Wiman Joseon and send embassies to the court of Han DynastyChina, there was probably some level of stable central authority. Korean historian Ki-baek Lee (1984, p. 24) also suggests that the kingdom's attempt to open direct contacts "suggests a strong desire on the part of Chin [Jin] to enjoy the benefits of Chinese metal culture." However, for the most part Wiman Joseon prevented direct contact between Jin and China.
King Jun of Gojoseon is reported to have fled to Jin after Wiman seized his throne and established Wiman Joseon. Some believe that Chinese mentions of Gaeguk or Gaemaguk (蓋馬國, Kingdom of armored horses) refers to Jin. Goguryeo is said to have conquered "Gaemaguk" in 26 AD, but this may refer to a different tribe in northern Korea.
Records are somewhat contradictory on Jin's demise: it either became the later Jinhan, or diverged into the Samhan as a whole. Archeological records of Jin have been found centered in territory that later became Mahan.
Archaeologically, Jin is commonly identified with the Korean bronze dagger culture, which succeeded the Liaoning bronze dagger culture in the late first millennium BCE. The most abundant finds from this culture have been in southwestern Korea's Chungcheong and Jeolla regions. This suggests that Jin was based in the same area, which roughly coincides with the fragmentary historical evidence. Artifacts of the culture are found throughout southern Korea and were also exported to the Yayoi people of Kyūshū, Japan.
The name of Jin continued to be used in the name of the Jinhan confederacy and in the name "Byeonjin," an alternate term for Byeonhan. In addition, for some time the leader of Mahan continued to call himself the "Jin king," asserting nominal overlordship over all of the Samhan tribes.