The northern part of its territory is now situated in eastern Slovakia (Zemplín region), while a smaller southern portion of the former county belongs to Hungary, as part of Borsod-Abaúj-Zemplén County.

Initially, the capital of the county was the Zemplín Castle (Hungarian: Zempléni vár, Slovak: Zemplínsky hrad), in the 13th century also Sárospatak (in Slovak: Potok, meaning stream, brook, 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 (which is now divided between Slovakia and Hungary by the Ronyva/Roňava stream; the Hungarian part is known in Slovak as Nové Mesto pod Šiatrom and the Slovak part is now a separate village called Slovenské Nové Mesto).

The southern half (including the bigger part of the divided Sátoraljaújhely) stayed in Hungary as the county of Zemplén.

In the early 20th century, the subdivisions of Zemplén county were: The towns of Sátoraljaújhely, Sárospatak, Tokaj and Szerencs are now in Hungary, except for a small northern part (about a quarter) of Sátoraljaújhely to the northeast of the Ronyva (Rožňava) stream in Slovakia, now a small village with its own artificial Slovak name Slovenské Nové Mesto.