After the death of Günther XL in 1552, his four sons initially ruled the land jointly.

William's part of the county included the city of Frankenhausen, which he chose as his residence, and the districts of Straußberg, Heringen and Kelbra.

Albrecht VII (1537–1605) received Rudolstadt and Frankenhausen and founded the Schwarzburg-Rudolstadt line.

[1] William's first marriage was on 6 April 1567 with Elisabeth (d. 23 November 1590), the daughter of Count Joachim of Schlick.

His second marriage was on 7 March 1593 with Clara (1571–1658), the daughter of Duke William the Younger of Brunswick-Lüneburg.