Knonau is a municipality in the district of Affoltern in the canton of Zürich in Switzerland.

Of the rest of the land, 16% is settled (buildings or roads) and the remainder (1.8%) is non-productive (rivers, glaciers or mountains).

Most of the population (as of 2000[update]) speaks German (92.9%), with Italian being second most common ( 2.6%) and English being third ( 1.1%).

In the 2007 election the most popular party was the SVP which received 36.2% of the vote.

[4] The historical population is given in the following table:[3] Knonau railway station is a stop of the Zürich S-Bahn on the line S5.