Rennerod lies in the Westerwald on Bundesstraße 54 between Limburg an der Lahn to the south and Siegen 30 km to the north. Bad Marienberg lies 10 km to Rennerod's northwest. Through the town flows the Holzbach. Northeast of the town is found the 613 m-high Alsberg, some 2 km north-northeast of the Breitenbach Reservoir on the Breitenbach, an eastern tributary to the river Nister.
