Count of Ostfriesland

The counts and princes of East Frisia from the noble East Frisian family Cirksena descended from a line of East Frisian chieftains from Greetsiel. The county came into existence when Emperor Frederick III raised Ulrich I the son of a local chieftain to the status of Imperial Count in 1464.

The most important ruler from the House of Cirksena was Edzard the Great (1462–1528), under whose leadership the Imperial County of East Frisia reached its greatest extent. During his reign the Reformation spread throughout East Frisia.

In 1654 the Cirksena were elevated to princes by the emperor. Charles Edzard, the last ruler from the House of Cirksena, died without issue during the night of 25/26 May 1744 (reportedly from a glass of buttermilk, which is said to have drunk after a hunt). Immediately thereafter, the county passed to King Frederick II of Prussia.

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Wikipedia