[1] Its county seat is Adel,[2] and its largest city is Waukee.

The county was named for George M. Dallas, Vice President of the United States under James K. Polk, the namesake of neighboring Polk County.

[3] The land that now forms Dallas County was ceded by the Sac and Fox nation to the United States in a treaty signed on October 11, 1842.

On January 13, 1846, the legislative body of the Iowa Territory authorized the creation of twelve counties in the Iowa Territory,[4] with general descriptions of their boundaries.

The county's population grew rapidly, with settlers coming to claim homesteads.

There were 16,529 housing units at an average density of 28 per square mile (11/km2).

The population ranking of the following table is based on the 2020 census of Dallas County.