Solothurn, canton, northwestern Switzerland. It is bounded by the cantons of Bern to the west and south, Jura to the west, Aargau to the east, and Basel-Landschaft (demicanton) to the north. It is drained by the Aare River and its tributaries. Consisting of territories acquired by Solothurn (q.v.), its capital city, from which it took its name, it has an irregular shape, including two completely detached districts bordering on France in the north. It also includes the foothills of the Jura Mountains and a plain along the Aare River valley, part of which extends into Bern canton.
Part of the Helvetic Republic after 1798, it became in 1803 one of the 19 cantons of the Swiss Confederation as reconstituted by Napoleon’s Act of Mediation. Although distinctly Roman Catholic, it did not join the Sonderbund (separatist league of Catholic cantons) in 1845, and it approved the federal constitutions of 1848 and 1874. The present cantonal constitution dates from 1887 but was substantially revised in 1895 and 1986.
Until the 19th century, the canton’s economic activities were mainly agricultural and pastoral. Although these are still important, the population is largely engaged in food processing and the manufacture of machinery, metal products, precision instruments, watches, and paper. A nuclear-power station began operation at Gösgen in 1979. The canton has excellent road and rail connections. Olten is a railway junction for direct lines from Geneva, Zürich, and Basel and the St. Gotthard Pass via Lucerne. The population is almost entirely German speaking, with about two-fifths Roman Catholic and one-third Protestant. Area 305 square miles (791 square km). Pop. (2007 est.) 248,613.