Neighbouring districts are (from north clockwise) Altenkirchen, Lahn-Dill, Limburg-Weilburg, Rhein-Lahn, the district-free city Koblenz, Mayen-Koblenz and Neuwied.

In 1974 in another reform the districts Oberwesterwaldkreis and Unterwesterwaldkreis were merged to form the Westerwaldkreis.

Together with the neighboring Rhein-Lahn district a partnership with the English county Northamptonshire was started in 1981.

Its highest elevation is the Fuchskaute, at 657 m, the lowest is near Diez in the valley of the Gelbach, at 150 m. The bottom part of the coat of arms show basalt pillars, as the Westerwald is of volcanic origin.

The green band in the middle represents the forests, the jug in the upper part the traditional pottery industry in the district.