Zemplén (Hungarian: Zemplén, Slovak: Zemplín, German: Semplin, Semmlin, Latin: Zemplinum) was an administrative county (comitatus) of the Kingdom of Hungary. 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.

Zemplén county shared borders with Poland (during some periods the with 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 Laborc and Bodrog flowed through the county. Its area was 6,269 km around 1910.

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).

Zemplén was one of the oldest counties of the Kingdom of Hungary. In the aftermath of World War I, in 1920 by the Treaty of Trianon the northern part of Zemplén county became part of newly formed Czechoslovakia. The southern half (including the bigger part of the divided Sátoraljaújhely) stayed in Hungary as the county of Zemplén. Following the provisions of the First Vienna Award, an additional part became part of Hungary again in November 1938. The Trianon borders were restored after World War II, and the Hungarian county Zemplén merged with Abaúj, the most of Borsod-Gömör and a little part of Szabolcs counties to form the present Borsod-Abaúj-Zemplén County.

Population by mother tongue

Census	Total	Hungarian	Slovak	Ruthenian	German	Other or unknown
1880	275,175	119,656 (44.73%)	102,730 (38.40%)	30,207 (11.29%)	12,977 (4.85%)	1,932 (0.72%)
1890	299,197	141,188 (47.19%)	107,477 (35.92%)	31,036 (10.37%)	15,511 (5.18%)	3,985 (1.33%)
1900	327,993	174,107 (53.08%)	106,114 (32.35%)	34,831 (10.62%)	8,072 (2.46%)	4,869 (1.48%)
1910	343,194	193,794 (56.47%)	92,943 (27.08%)	39,033 (11.37%)	9,749 (2.84%)	7,675 (2.24%)

Population by religion

Census	Total	Roman Catholic	Greek Catholic	Calvinist	Jewish	Lutheran	Other or unknown
1880	275,175	100,091 (36.37%)	83,696 (30.42%)	53,252 (19.35%)	31,622 (11.49%)	6,416 (2.33%)	98 (0.04%)
1890	299,197	110,982 (37.09%)	92,220 (30.82%)	58,671 (19.61%)	30,491 (10.19%)	6,780 (2.27%)	53 (0.02%)
1900	327,993	123,967 (37.80%)	101,053 (30.81%)	64,457 (19.65%)	31,533 (9.61%)	6,807 (2.08%)	176 (0.05%)
1910	343,194	132,395 (38.58%)	103,118 (30.05%)	67,557 (19.68%)	33,041 (9.63%)	6,822 (1.99%)	261 (0.08%)

In the early 20th century, the subdivisions of Zemplén county were:

Districts (járás)
District	Capital
Bodrogköz	Királyhelmec (now Kráľovský Chlmec)
Gálszécs	Gálszécs (now Sečovce)
Homonna	Homonna (now Humenné)
Mezőlaborc	Mezőlaborc (now Medzilaborce)
Nagymihály	Nagymihály (now Michalovce)
Sárospatak	Sárospatak
Sátoraljaújhely	Sátoraljaújhely
Szerencs	Szerencs
Szinna	Szinna (now Snina)
Sztropkó	Sztropkó (now Stropkov)
Tokaj	Tokaj
Varannó	Varannó (now Vranov nad Topľou)
Urban districts (rendezett tanácsú város)
Sátoraljaújhely

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.

• Demetrius Futaki (d. 1372), born at Mézes in Zemplén county