Erlinsbach is a municipality in the district of Aarau of the canton of Aargau in Switzerland.

Aarau is a town, a municipality, and the capital of the northern Swiss canton of Aargau. The town is also the capital of the district of Aarau. It is German-speaking and predominantly Protestant. Aarau is situated on the Swiss plateau, in the valley of the Aare, on the river's right bank, and at the southern foot of the Jura Mountains, and is west of Zürich, 58 kilometres (36 mi) south of Basel and 65 kilometres (40 mi) northeast of Bern. The municipality borders directly on the canton of Solothurn to the west. It is the largest town in Aargau. At the beginning of 2010 Rohr became a district of Aarau.