Önsbach is the second-largest district ("Stadtteil") of the major district town ("Kreisstadt") of Achern in the north of Ortenaukreis, located in the Black Forest.

Önsbach is located in northern Ortenau, south of the town of Achern.

The earliest documentary evidence of Önsbach appears in a 1225 Papal bull of Honorius III in which the town is called Ongersbac where the cloister of Ettenheim held property.

Ortenau, in which Önsbach is located, became part of the Grand Duchy of Baden after the Fourth Peace of Pressburg (1805).

It consists of a birds foot with three fore-talons and one hind talon on a red background.