Isenburg-Birstein was the name of two German historical states based around Birstein in southeastern Hesse, Germany. The first "Isenburg-Birstein" was a County and was created as a partition of Isenburg-Büdingen-Birstein in 1628. It was merged into Isenburg-Offenbach in 1664. The second "Isenburg-Birstein" was a Principality, created as a partition of Isenburg-Offenbach in 1711. It was renamed the "Principality of Isenburg" in 1806.
Read more about Isenburg-Birstein: Counts of Isenburg-Birstein (1628 - 1664), Count of Isenburg-Birstein (1711 - 1744), Princes of Isenburg-Birstein (1744 - 1806)