There were two different Counties of the same name. The first (1341–1511) was a partition of Isenburg-Cleberg, and was partitioned into Isenburg-Büdingen-Birstein and Isenburg-Ronneburg in 1511. The second (1628–1806) was a partition of Isenburg-Büdingen-Birstein. It was partitioned between itself, Isenburg-Meerholz and Isenburg-Wächtersbach in 1673, and was mediatised to Isenburg in 1806. In 1816 Isenburg was partitioned between the Grand Duchy of Hesse-Darmstadt and the Electorate of Hesse-Kassel.
Count Ernest Casimir (1801-1848) was elevated to the rank of prince by Louis II, Grand Duke of Hesse, in 1840. Since then, the name of the branch is spelled Ysenburg and Büdingen, to distinguish it from the princes of Isenburg from the Isenburg-Birstein branch.
