Kim is Korea’s most common surname, written 김 and with the Chinese character 金, whose ordinary meaning is “gold” (also metal). That character gloss is agreed across Ancestry’s Korean entry and Korean/Wikipedia summaries. It is not an English nickname invented in Ohio; it is a Korean clan name that many separate bon-gwan (clan seats) share.
US Census Kim also includes some Chinese or other romanizations of 金. The family-friendly lead remains: Korean lineage name whose written character means gold. Do not overclaim a single fairy-tale founder for every Kim—Korean history records many Kim clans under one spelling.