In 1920 the Treaty of Trianon assigned the part of Komárom county north of the Danube to Czechoslovakia (Komárno region). The southern part stayed in Hungary and merged with the southern part of Esztergom county to form Komárom-Esztergom county.

In 1938, the Czechoslovak part became part of Hungary by the First Vienna Award. Komárom county was recreated, which included, besides the territory of pre-1920 Komárom County, most of the Rye Island. After World War II, the pre-war situation was reestablished, except that the name of the Hungarian part became Komárom County again. This county was renamed to Komárom-Esztergom County in 1992. The part of the former county north of the river Danube is now in Slovakia, is part of the Nitra region and is largely identical with the Komárno district.