Walnut Township covers an area of 36.62 square miles (94.8 km2) and contains one incorporated settlement, Waukee.

According to the USGS, it contains two cemeteries: Hoff and Waukee.

The stream of Little Walnut Creek runs through this township.

Walnut Township contains one airport or landing strip, Robel Field.

This article about the geography of Dallas County, Iowa is a stub.