A lordship in the Holy Roman Empire, in northeastern Germany; the town of Barby is on the River Elbe, southeast of Magdeburg.
The lordship belonged to the Abbey of Quedlinburg, and in the 12th century was held in fief by the Lords of Arnstein (which is in the Harz). A branch of the Arnstein family survived in Barby until 1659, with the title of Count from 1497. Barby belonged to the Upper Saxon Circle in the Empire In 1659, when the family died out, Barby itself went to Saxe-Weissenfels (and later reverted to the Electorate of Saxony), while other parts of the County went to Brandenburg and Anhalt-Zerbst. In 1807 Barby became part of the Kingdom of Westphalia and in 1815 of Prussia. It is now in Sachsen-Anhalt.