The village lies between the north bank of the Aare river and the south slope of the Mount Gislifluh (elev.

Auenstein has an area, as of 2006[update], of 5.7 square kilometers (2.2 sq mi).

Of the rest of the land, 17.6% is settled (buildings or roads) and the remainder (4.9%) is non-productive (rivers or lakes).

[3] Neighboring municipalities are Oberflachs and Veltheim to the north, Möriken-Wildegg to the east, Rupperswil to the south, Biberstein to the west, and Thalheim to the northwest.

[4] The name probably comes from the small Castle Auenstein on the river Aare, which was built in about 1200 (probably by the lords of Gowenstein).

The castle, which was in the possession of the Lords of Rinach until the early 14th century, was burnt down by the Bernese in 1389 as part of the war between the Old Swiss Confederacy and the Habsburgs.

Castle Auenstein is located on a small cliff on the banks of the Aare.

[3] The age distribution, as of 2008[update], in Auenstein is; 128 children or 8.8% of the population are between 0 and 9 years old and 157 teenagers or 10.7% are between 10 and 19.

[8] About 74.4% of the total households were owner occupied, or in other words did not pay rent (though they may have a mortgage or a rent-to-own agreement).

[10] The historical population is given in the following table:[4] As of  2007[update], Auenstein had an unemployment rate of 1.9%.

[3] From the 2000 census[update], 230 or 16.9% were Roman Catholic, while 883 or 65.0% belonged to the Swiss Reformed Church.