The Lordship of Myllendonk (sometimes spelled "Millendonk") was an estate of the Holy Roman Empire, located in western North Rhine-Westphalia, Germany.

It was bordered by the Duchy of Jülich to the west and north, the Lordship of Dyck to the south, and the Archbishopric of Cologne to the east and southeast.

The line was annexed to the Pesch Myllendonk family in 1263, and in c. 1350 passed to the House of Mirlaer which renamed itself to Myllendonk-Mirlaer.

The Counts of Ostein ruled Myllendonk until 1794 when the French conquered the German territory on the western side of the Rhine River.

The following year the Lordship was abolished and the territory was annexed into the newly created Province of Rhineland.