Untersiggenthal is a municipality in the district of Baden in the canton of Aargau in Switzerland, located in the Limmat Valley (German: Limmattal).

Of the rest of the land, 18.8% is settled (buildings or roads) and the remainder (3.8%) is non-productive (rivers or lakes).

[3] The blazon of the municipal coat of arms is Gules two Keys in saltire Argent.

[3] The age distribution, as of 2008[update], in Untersiggenthal is; 685 children or 10.7% of the population are between 0 and 9 years old and 766 teenagers or 11.9% are between 10 and 19.

[8] The historical population is given in the following table:[7] The ruined Freudenau castle and the neolithic/Bronze Age settlement at Heidenküche are listed as Swiss heritage sites of national significance.

[3] From the 2000 census[update], 2,919 or 47.6% are Roman Catholic, while 1,727 or 28.2% belonged to the Swiss Reformed Church.