megye (county), east-central Hungary. It is bounded by the counties of Heves and Borsod-Abaúj-Zemplén to the north, Hajdú-Bihar and Békés to the east, Csongrád to the south, Bács-Kiskun to the southwest, and Pest to the west. The county seat is Szolnok, and the principal cities are Jászberény, Mezőtúr, Karcag, and Törökszentmiklós.

Situated in the Great Alfold (Great Hungarian Plain, or Nagy Magyar Alföld), Jász-Nagykun-Szolnok is drained from north to south by the Tisza River. The Körös River flows on the county's southern fringe, while in the northwest the Zagyva River crosses the Jászság, a marginal depression of the Alfold, which extends into Pest county and produces vegetables, fruit, and poultry for the Budapest market. East of the Tisza is the Nagykunság, a loess plain covered with a high-grade chernozem (black) soil. It is mostly farmland, with high yields of wheat and corn (maize); rice is grown in irrigated areas along the river. Crude oil and natural gas reserves are significant in the region between Szolnok and Berekfürdő. Clay and sand mining is also considerable. The county is Hungary's least-industrialized area.

Jász-Nagykun-Szolnok is rich in thermal and mineral waters, with more than 150 warm springs and wells, many of which were discovered while drilling for petroleum. Principal resorts include Jászberény, Jászapáti, Szolnok, and Tiszafüred. Berekfürdő and Cserkeszőlő are known for their iodine-rich waters. Area 2,155 square miles (5,582 square km). Pop. (2004 est.) 413,000.