Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Oldenburg (Low German: Ollnborg) is a historical state in today''s Germany named for its capital, Oldenburg. Oldenburg existed from 1180 until 1918 as a county, duchy and grand duchy. It was located near the mouth of the River Weser. Its ruling family was the House of Oldenburg, which also acquired Denmark and Russia.