It lies in central Hungary and shares borders with the Hungarian counties Pest, Heves, Borsod–Abaúj–Zemplén, Hajdú–Bihar, Békés, Csongrád, and Bács–Kiskun.

The county is named after the Ossetians (Jasz) and Cumans (Kun) who settled there, along with Szolnok.

It consists of the unification of the coat of arms of Jászság, Nagykunság and former Exterior-Szolnok County.

The upper part is divided into two equally spaced vertices from top to bottom.

56,000 persons in Jász-Nagykun-Szolnok County did not declare their ethnic group at the 2011 census.