"Nassau-Usingen was a county of the Holy Roman Empire in the Upper Rhenish Circle that became a principality in 1688.
The origin of the county lies in ...
the medieval county of Weilnau that was acquired by the counts of Nassau-Weilburg in 1602.
That county was divided in 1629 into the lines of Nassau-Weilburg, Nassau-Idstein and Nassau-Saarbrücken that was divided only 30 years later in 1659.
The emerging counties were Nassau-Saarbrücken, Nassau-Ottweiler and Nassau-Usingen. At the beginning of the 18th century, three of the Nassau lines died out and Nassau-Usingen became their successor (1721 Nassau-Idstein, 1723 Nassau-Ottweiler und 1728 Nassau-Saarbrücken)." - (en.wikipedia.org 10.08.2021)
