Württemberg-Neuenstadt was the name of two branch lines of the ducal House of Württemberg in the 17th and 18th century. It was named after the town of residence, Neuenstadt.
The first branch line of this name came into existence after a Fürstbrüderlicher Vergleich - a mutual agreement made between ducal brothers on 7 June 1617 (Julian calendar: 28 May). Under the agreement, the sons of Duke Friedrich I split the inheritance such that the eldest son, Johann Frederick, assumed borony over the Duchy of Württemberg while his remaining brothers assumed possession of other ducal properties. The second youngest son, Frederick Achilles, was bequeathed Neuenstadt Castle and an annual endowment of 10,000 guilder. After the death of Frederick Achilles in 1631, who was still unmarried, the castle returned to the main line of the duchy.
The second branch line came into existence in 1649, after the restitution of Württemberg following the Thirty Years’ War. Under the inheritance agreement of 7 October 1649 (27 September under the Julian calendar) Duke Eberhard III left his brother Frederick possession of Neuenstadt, Möckmühl and Weinsberg, although this was without sovereignty as this was passed on to Eberhard.
Duke Frederick was married to Clara Augusta, daughter of August the Younger of Brunswick. The couple brought 12 children into the world, of which three male children survived to adulthood: Frederick August, Ferdinand Wilhelm and Carl Rudolf. Duke Frederick died in 1682, outlived by his widow who resided in Neuenstadt and her widow’s residence of Weißenhof by Weinsberg until 1700 when she died.