20th century census data

The last antebellum census in Hungary, 1910. The four counties of Hungary that covered
the territory what we now call Carpathian Ruthenia were Ung, Bereg, Ugocsa and Máramaros.

Ugocsa and Máramaros counties were split between Czechoslovakia and Romania in 1920 after the disintegration of the Austro-Hungarian Empire, who lost the war. Hungary annexed their northern parts from the short lived Ruthenian state in 1939, and their southern parts from Romania in 1940. The northern parts now belong to the Ukraine as a successor state to the Soviet Union.

Ung and Bereg were part of Czechoslovakia after 1920, except a small part of Bereg that stayed with Hungary. Hungary annexed their lower or southern parts from Czechoslovakia in 1938, and their upper or northern parts from the Ruthenian state in 1939. The vast majority of these counties now belong to the Ukraine, while a western strip belongs to Slovakia.