ORTNAU, a county of Germany, in the circle of Swabia, lying along the Rhine, and separating it from Alsace. It is bounded on the south by Breislaue, on the north by the margravate of Baden, and on the east by the duchy of Wurtemberg. It contains three imperial towns; namely, Offenburg, Gengenbach, and Zell. It belongs partly to the house of Austria, partly to the bishopric of Spire, and partly to the county of Hannau.