||Zemplén (Hungarian: Zemplén, German: Semplin, Latin: Zemplinum) is the name of a historic administrative county of the Kingdom of Hungary. Its territory is presently situated in eastern Slovakia under the name of Zemplín. Most of the county's territory is today in Slovakia except the southern portions of the county are still in Hungary, in the county of Borsod-Abauj-ZemplenZemplén county shared borders with Poland (during some periods the Austrian crownland Galicia) and the Hungarian counties Sáros, Abaúj-Torna, Borsod, Szabolcs and Ung. It was situated in the easternmost strip of what is now Slovakia (except for the region between Vihorlatské vrchy and the Latorica river), plus a strip along the Bodrog and Tisza rivers in present-day Hungary. The rivers Laborec and Bodrog flowed through the county. Its area was 6,269 km² around 1910.
Initially, the capital of the county was the Zemplín Castle, in the 13th century also Sárospatak (in Slovak: Potok, hence the alternative name of the county comitatus de Potok). Since the Late Middle Ages the capital was the town of Zemplén, and since 1748 was Sátoraljaújhely (Slovak: Nové Mesto pod Šiatrom).
Zemplén was one of the oldest counties of the Kingdom of Hungary. In 1918 (confirmed by the Treaty of Trianon 1920), the northern part of the county became part of newly formed Czechoslovakia. The southern half (including the bigger part of the divided Sátoraljaújhely) stayed in Hungary as the county Zemplén. One of its main cities is Szinna.