The Duchy of Oldenburg named after its capital, the town of Oldenburg was a state in the north-west of present-day Germany. The counts of Oldenburg died out in 1667, after which it became a duchy until 1810, when it was annexed by the First French Empire. It was located near the mouth of the River Weser.

Oldenburg (German pronunciation: [ˈɔldn̩bʊʁk] ; Northern Low Saxon: Ollnborg) is an independent city in the state of Lower Saxony, Germany. The city is officially named Oldenburg (Oldb) (Oldenburg in Oldenburg) to distinguish from Oldenburg in Holstein.