Aargau, canton, northern Switzerland. It borders Germany to the north and is bounded by the demicanton of Basel-Landschaft and by the cantons of Solothurn and Bern to the west, Lucerne to the south, and Zug and Zürich to the east. It forms the northeastern section of the great Swiss Plateau between the Alps and the Jura Mountains, taking in the lower course of the Aare River, whence its name. Its valleys alternate with pleasantly wooded hills.
In 1415 the region was taken by the Swiss Confederation from the Habsburgs, whose ancestral seat was near Aarau (q.v.), now the cantonal capital. Bern kept the southwestern portion. In 1798 the Bernese part became Aargau canton of the Helvetic Republic, and the remainder formed the canton of Baden. In 1803 the two halves (and Frick, ceded to the Helvetic Republic by Austria in 1802) were united and admitted to the Swiss Confederation as Aargau canton.
One of the most fertile parts of Switzerland, Aargau includes among its principal economic activities dairying, fruit and cereal growing, and straw plaiting. Industries include electrical engineering, food processing, and the manufacture of machines, chemicals, and metal and electrical products, precision instruments, and cement. The canton is also the site of nuclear power stations. The picturesque landscape, ancient castles, and rich museums of the canton attract considerable tourist traffic, as do the hot springs at Schinznach Bad Baden and Zurzach. The population is almost exclusively German speaking. A small majority of the people are Roman Catholic. Area 542 square miles (1,404 square km). Pop. (2007 est.) 574,813.