Lower Isenburg (German: Nieder-Isenburg) was the name of a state of the Holy Roman Empire, based around Isenburg in modern Rhineland-Palatinate, Germany. The County of Lower Isenburg emerged as a partition of Isenburg-Isenburg in 1218 (1199). Lower Isenburg was informally mediate to the Abbey of Fulda, although the claim was not pursued for centuries. The Isenburgs were one of the oldest families in the Westerwald and despite partitioning into several lines Lower Isenburg was the residence of choice for those in the Rhineland. In 1502 Lower Isenburg was partitioned into Isenburg-Grenzau and Isenburg-Neumagen. Isenburg-Neumagen became extinct in 1554 and Isenburg-Grenzau in 1664, and the Counts of Wied and the barons of Walderdorff divided the County between them.