It was situated approximately along the line Poltár, Losonc (today Lučenec), Szécsény and Vác.

In the aftermath of World War I, the part of Nógrád county north of the river Ipeľ/Ipoly became part of newly formed Czechoslovakia (as Novohrad county), as recognized by the concerned states in 1920 by the Treaty of Trianon.

After World War II, the Trianon borders and Nógrád-Hont County were restored.

Since 1996, it has been part of the Slovak administrative unit Banska Bystrica region.

In the early 20th century, the subdivisions of Nógrád county were: The municipalities of Lučenec, Fiľakovo and Halič are now in Slovakia.