Yu Jin was from Juping County (鉅平縣), Taishan Commandery (泰山郡), which is in present-day Tai'an, Shandong.
In 192,[REF] after the warlord Cao Cao took charge of Yan Province, Yu Jin and his fellow volunteers were appointed as doubos (都伯; a military officer in charge of 100 soldiers) and placed under the command of Wang Lang.