| Conventional Long Name: | County of Nassau-Usingen |
| Common Name: | Nassau-Usingen |
| Status: | State of the Holy Roman Empire and later Confederation of the Rhine |
| Empire: | Holy Roman Empire |
| Government Type: | County/Principality |
| Year Start: | 1659 |
| Event End: | Merged with Nassau-Weilberg to form the Duchy of Nassau |
| Date End: | August 30, |
| Year End: | 1806 |
| Event1: | Became principality |
| Date Event1: | 1688 |
| Event2: | Joined the Confederation of the Rhine |
| Date Event2: | July 17, 1806 |
| S1: | Duchy of Nassau |
| Capital: | Usingen |
| Currency: | Guilder |
| Leader1: | Walrad (first) |
| Year Leader1: | 1659-1702 |
| Title Leader: | Count/Prince |
| Today: | Germany |
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. However, the division became effective only thirty 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). In 1735, Nassau-Usingen was divided again into Nassau-Usingen and Nassau-Saarbrücken. In 1797, Nassau-Usingen inherited Nassau-Saarbrücken.
On July 17, 1806, the counties of Nassau-Usingen and Nassau-Weilburg joined the Confederation of the Rhine. Under pressure from Napoleon, both counties merged to become the Duchy of Nassau on August 30, 1806, under joint rule of Prince Frederick August of Nassau-Usingen and his younger cousin Prince Frederick William of Nassau-Weilburg. As Frederick August had no heirs, he agreed that Frederick William should become sole ruler after his death. However, Frederick William died from a fall on the stairs at Schloss Weilburg on 9 January 1816, and it was his son William who became duke of a unified Nassau.
The title has been carried in pretense by Prince Frederick August's half-brother Karl Philip's line.
| Ruler | Born | Reign | Ruling part | Consort | Death | Notes | |
|---|---|---|---|---|---|---|---|
| Walrad | 25 February 1635 Roermond Seventh son of William Louis, Count of Nassau-Saarbrücken and Anna Amalia of Baden-Durlach | 1659 – 17 October 1702 | County of Usingen (1659–88) Principality of Usingen (1688–1702) | Catherine Françoise of Croÿ-Roeulx 16 June 1678 Mechelen three children Magdalena Elizabeth of Löwenstein-Wertheim-Rochefort 1686 no children | 17 October 1702 Usingen aged 66 | ||
| William Henry | 2 May 1684 's-Hertogenbosch Son of Walrad and Catherine Françoise of Croÿ-Roeulx | 17 October 1702 – 14 February 1718 | Principality of Usingen | Charlotte Amalia of Nassau-Dillenburg 15 April 1706 Dillenburg nine children | 14 February 1718 Usingen aged 33 | ||
| Regency of Charlotte Amalia of Nassau-Dillenburg (1718–1734) | Charles was the only heir, but in 1741 he divided the inheritance, and gave Saarbrücken to his brother (raised as a principality), and retained Usingen. | ||||||
| Charles | 31 December 1712 Usingen First son of William Henry, Prince of Nassau-Usingen and Charlotte Amalia of Nassau-Dillenburg | 14 February 1718 – 21 June 1775 | Principality of Usingen | Christine Wilhelmine of Saxe-Eisenach 26 December 1734 four children Magdalene Gross of Wiesbaden after 1740 (morganatic) four children | 21 June 1775 Biebrich aged 62 | ||
| Charles William | 9 November 1735 Usingen First son of Charles and Christina Wilhelmina of Saxe-Eisenach | 21 June 1775 – 17 May 1803 | Principality of Usingen | Caroline Felizitas of Leiningen-Dagsburg 16 April 1760 one child | 17 May 1803 Biebrich aged 67 | Left no descendants. He was succeeded by his brother. | |
| In 1783, the heads of various branches of the House of Nassau sealed the Nassau Family Pact (German: Erbverein) to regulate future succession in their states, and to establish a dynastic hierarchy whereby the Prince of Orange-Nassau-Dietz was recognised as President of the House of Nassau.[1] | |||||||
| Frederick Augustus | 23 April 1738 Usingen Second son of Charles and Christine Wilhelmine of Saxe-Eisenach | 17 May 1803 – 24 March 1816 | Principality of Usingen | Louise of Waldeck 9 June 1775 seven children | 24 March 1816 Wiesbaden aged 77 | ||
| 30 August 1806 – 24 March 1816 | Duchy of Nassau | ||||||
| Nassau-Usingen united with Nassau-Weilburg to form the Duchy of Nassau | |||||||