Isenburg was a region of Germany located in southern present-day Hesse, located in territories north and south of Frankfurt. The states of Isenburg emerged from the Niederlahngau (located in the Rhineland-Palatinate), which partitioned in 1137 into Isenburg-Isenburg and Isenburg-Limburg-Covern. These countships were partitioned between themselves many times over the next 700 years.
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…