House of Isenburg

The House of Isenburg was an old aristocratic family of medieval Germany, named after the castle of Isenburg in North Rhine-Westphalia. Occasionally referred to as the House of Rommersdorf before the 12th Century, the house originated in the Hessian comitatus of the Niederlahngau in the 10th Century. It partitioned into the lines of Isenburg-Isenburg and Isenburg-Limburg-Covern in 1137, before partitioning again into smaller units, but by 1500 only the lines of Isenburg-Büdingen (in Upper Isenburg) and Lower Isenburg remained.

In 1664 the Lower Isenburg branch died out. The Büdingen line continued to partition, and by the beginning of the 19th Century the lines of Isenburg-Büdingen, Isenburg-Birstein, Isenburg-Meerholz and Isenburg-Wächtersbach existed. The Principality of Isenburg was created in 1806 when the princely Birstein line mediatised the comital others, and the principality itself was mediatised in 1814 by the Congress of Vienna with its territories annexed to the Grand Duchy of Hesse.