Saxe-Weissenfels

Saxe-Weissenfels () was a Duchy of the Holy Roman Empire from 1656 until 1746 with its residence at Weißenfels. Ruled by a cadet branch of the Albertine House of Wettin, the duchy passed to the Electorate of Saxony upon the extinction of the line. thumb|left|Neu-Augustusburg Castle, Weissenfels John George I of Wettin, Saxon prince-elector from 1611 to 1656, had disposed in his testament that while his eldest son John George II would succeed him as elector, his younger brothers should be vested with secundogeniture duchies as an appanage. Therefore, upon his death the Duchies of Saxe-Zeitz, Saxe-Merseburg and Saxe-Weissenfels arose, the latter was granted to the second eldest son Augustus, who already served as the Protestant administrator of the Archbishopric of Magdeburg since 1638, then residing at Halle. From about 1660 he had the Baroque Neu-Augustusburg residence built at Weissenfels.

Beside Weissenfels the duchy comprised the ämter of Freyburg, Sachsenburg (present-day Oldisleben), Sangerhausen, Eckartsberga, Weißensee and Langensalza. Duke Augustus enlarged its territory by several lordships originally held by the Magdeburg archbishops and adjudicated to Saxony by the 1635 Peace of Prague, including the immediate lordship of Querfurt as well as the exclaves of Jüterbog, Dahme and Burg.