The Untertaunus region was part of the Earldom ofKatzenelnbogen. From 1816 onward, the whole area of the district became part of the Duchy of Nassau. After the 1866Austro-Prussian war, Nassau was annexed byPrussia and formed the new province ofHesse-Nassau.
In 1867, the province was divided into districts. Therefore, the districts of Rheingau and Untertaunus were created.
After the Second World War and the creation ofHesse in 1946, these two districts remained unchanged. Only in 1977, because administrative borders were redrawn, the districts of Rheingau and Untertaunus merged and thus formed the Rheingau-Taunus district.
The coat of arms combines the coat of arms of the two former districts - in the bottom right theMainz wheel taken from the Rheingau district, in the top left the lion ofNassau from the former Untertaunuskreis.