|County of Lower Isenburg|
|1218 - 1806|
Counts of the Wetterau
|Partitioned from Isenburg-Isenburg||1218|
|To Isenburg-Grenzau and -Neumagen||1502|
|Isenburg-Grenzau extinct; seat to Trier; land to Walderdorff and Wied||1664|
Lower Isenburg was created as a partition of Isenburg-Isenburg in 1218 and slowly gained in size and rose to prominence over the centuries. In 1495 at the Reichstag in Worms the importance of Lower Isenburg increased greatly when Gerlach III was chosen to hold the Emperor's banner before the Princes of the Empire. In 1502 Lower Isenburg was divided into the lines of Isenburg-Grenzau, ruled by Gerlach, and Isenburg-Neumagen, ruled by his brother Salentin VI.
In 1512 Gerlach and Salentin joined the elector-Archbishops of Cologne, Mainz and Trier; the Elector Palatine; the imperial postmaster Thurn and Taxis; the Duke of Arenberg; the Teutonic Order at Coblenz; the prince of Nassau-Beilstein; and the arch-treasurer of the Empire Sinzendorf; in forming the Electoral Rhenish Circle.
Isenburg-Neumagen became extinct in 1554 and was inherited by Sayn-Homburg, leaving Isenburg-Grenzau the full vote in the Circle Diet. In 1664 Isenburg-Grenzau also became extinct. With no other lines of Lower Isenburg, the Archbishop of Trier, barons of Walderdorff supported by the Abbot of Fulda and the Count of Wied each claimed Lower Isenburg. The Archbishops gained the Lower Isenburg seat in the diet, and Walderdorff and Wied divided the territories of Lower Isenburg between them. In 1806 Lower Isenburg was annexed to the Grand Duchy of Berg.
|Electoral Rhenish Circle|
|Arenberg | Beilstein | Coblenz | Cologne | Lower Isenburg | Mainz | Palatinate|
Rheineck | Thurn and Taxis | Trier
|Gelnhausen | Neuenahr | Reifferscheid | Selz | St Maximin|