John died childless in 1328 and Henry inherited Nassau-Dillenburg. Henry moved to Dillenburg and his descendants are known as the Nassau-Dillenburg line.
This division created a new principality of Nassau-Siegen. It belonged to the Lower Rhenish–Westphalian Circle. After John VII died in 1628, the country was divided:
His eldest son, John VIII, who had converted to Catholicism, received the part of the county south of the riverSieg and the original castle in Siegen. John VIII was the founder of the Catholic line of Nassau-Siegen.
John Maurice, who remained Protestant, received the part of the county north of the Sieg. He was the founder of the Protestant line of Nassau-Siegen and he converted the former Franciscan monastery into a new residence, called the "Lower Castle", which was reconstructed after having burnt down at large parts in 1695. John Maurice spent most of his time away from Siegen, since he was governor of Dutch Brazil and later of the Prussian province of Cleves, Mark, and Ravensberg. Between 1638 and 1674, his brother George Frederick ruled the Protestant part of the country.
In 1652, John Francis Desideratus of the Catholic line was elevated to Imperial Prince. Count Henry II of the Protestant line married Marie Elisabeth of Limburg-Styrum, who brought the Lordship of Wisch in the County of Zutphen into the marriage. In 1664, John Maurice of the Protestant line was also elevated to Imperial Prince. In 1734, the Protestant line died out with the death of Frederick William II. Nassau-Siegen was reunited under William Hyacinth, the last ruler of the Catholic line. When he died in 1743, Nassau-Siegen had died out in the male line, and the territory fell to Prince William IV of the Orange-Nassau-Dietz line, who thereby reunited all the lands of the Ottonian line of the House of Nassau.
The principality consisted of the districts of Siegen, Netphen, Hilchenbach, and Freudenberg. From 1628-1734, the Protestant part consisted of the districts of Hilchenbach and Freudenberg and a half the district of Siegen. At the time, the Catholic half of the district of Siegen was called the district of Hayn. The Catholic part of the county consisted of the district of Netphen and the other half of the district of Siegen. In the north, it bordered the Duchy of Westphalia. In the west, it bordered Wildenburg and Sayn-Altenkirchen. In the south, it bordered Nassau-Dillenburg and in the east Wittgenstein-Wittgenstein.
