Nienburg (ˈniːn.ˌbʊʁk) is a district (Landkreis) in Lower Saxony, Germany. It is bounded by (from the west and clockwise) the districts of Diepholz, Verden, Heidekreis, Hanover and Schaumburg, and by the state of North Rhine-Westphalia (district of Minden-Lübbecke).
From the early Middle Ages to the end of the 16th century this region was the heart of the County of Hoya. The ruling family became extinct in 1582, and the central and southern parts of the county were annexed by the Lüneburg branch of the duchy of Brunswick-Lüneburg. In 1705 the area of Nienburg and Hoya became subordinate to Hanover.
In 1866 the Kingdom of Hanover was annexed by Prussia. The Prussian government established the districts of Nienburg and Stolzenau, which were merged in 1932.
The earliest official mention of Nienburg/Weser dates from the year 1025, when Milo, the Canon of Minden, apparently made a gift of his property in Nienburg to the Minden church. Since this early mention spoke of N