By the Peace of Westphalia the Prince-Archbishopric was transformed into the Duchy of Bremen in 1648, which - together with the Principality of Verden - was first given as a prey for its participation in the Thirty Years' War to be ruled in personal union by the Swedish Crown.

It was Bremen-Verden's government which commissioned the drainage, cultivation and colonisation of the moorlands, first under the responsibility of Moor Commissioner Jürgen Christian Findorff (1720–1792).

In 1785-89 Findorff prompted - after his own design - the construction of the Lutheran church of today's Grasberg on a sandy grass-covered hill (c. 5 m above sea level), giving the name to Grasberg (literally in English: grass mount), serving as a parish church for 12 newly founded villages in the lower moorlands.

The Lutheran church houses a rare treasury, the only surviving small scale urban pipe organ created by the famous Arp Schnitger, originally commissioned by an orphanage in Hamburg in 1694.

The Hanoveran Duchy of Bremen, including the already existing municipalities now component of Grasberg, changed occupation several times during the Napoléonic Wars.