Mermuth is an Ortsgemeinde – a municipality belonging to a Verbandsgemeinde, a kind of collective municipality – in the Rhein-Hunsrück-Kreis (district) in Rhineland-Palatinate, Germany. It belongs to the Verbandsgemeinde Hunsrück-Mittelrhein, whose seat is in Emmelshausen.

The municipality lies in the Hunsrück. Mermuth distinguishes itself by its quiet location off any thoroughfare; it can only be reached over a short branch road that leads nowhere else. The municipal area is framed by the two stream valleys each side, the Ehrbach and Baybach valleys, both of which can be reached over pathways from the village. The two entrances into the Ehrbach gorge are especially charming. In a wooded area north of the village stands the mediaeval Rauschenburg, a castle ruin.

Mermuth lies roughly 9.5 km southwest of the Rhine at Boppard and 6 km south-southeast of the Moselle at Brodenbach. The municipal area measures 490 ha and the municipality's elevation is 340 m above sea level.

Mermuth may well be one of the Hunsrück's oldest settlements. The name is traced back to the Celtic words merre (“water”) and munt (“hole”). archaeological finds confirm early settlement.

Beginning in 1794, Mermuth lay under French rule. In 1815 it was assigned to the Kingdom of Prussia at the Congress of Vienna. Since 1946, it has been part of the then newly founded state of Rhineland-Palatinate.

Also worthy of mention is the Mermuther Feiertag (“Mermuth Day of Celebration”). It has been held for many generations in the Virgin Mary’s honour. According to oral tradition, a pledge was made, after the village had been beset by a whole series of fires over a short time – some caused by troops in the Thirty Years' War – to keep this day to secure the protection of the “Mother of God”.

The council is made up of 6 council members, who were elected by majority vote at the municipal election held on 7 June 2009, and the honorary mayor as chairwoman.

Mermuth's mayor is Christian Busch.