Lordship in the Holy Roman Empire. The town of Büdingen is in central Germany, northwest of Gelnhausen, southeast of Nidda, and northeast of Frankfurt. The lords were also keepers of an Imperial forest (now in Hessen) that lay south of the Vogelsberg, and between the Rivers Nidda, in the west, Kinzig, in the south, and Salz, in the east.
The original lords may have been related to their principal successors, the family of Isenburg. When the last of the original family died in 1240, his inheritance was divided among several sons-in-law, among them the Count of Hohenlohe-Brauneck, but it was the family of Isenburg-Grunzau that gathered together the divided lands, a task not completed until 1376. During the 15th century the Counts of Isenburg-Büdingen, as they became known in 1442, expanded their territory, to include half of Offenbach, on the Main above Frankfurt. They even crossed the Main to acquire Dreiech. This enlarged territory became known as Ober-Isenburg.
The Counts followed the usual German custom of partitioning lands amongst the male heirs; the result was that there were several lines of the family in Ober-Isenburg. The head of the senior line, Isenburg-Birstein, became a Prince of the Empire in 1744, and in 1806 the then Prince became Prince of Isenburg and a member of the Confederation of the Rhine. The junior branches of the family were mediatised, among them the Count of Ysenburg & Büdingen, a line whose head was made a Hessian Prince in 1840.
The Prince of Isenburg was himself mediatised in 1815, the eastern part of his principality becoming part of Electoral Hesse, but most of it joining the Grand Duchy of Hesse.