Dallas County is a county located in the U.S. state of Iowa. As of the 2020 Census, the population was 99,678, making it the seventh-most populous county in Iowa. Between 2010 and 2020, it was the fastest growing county in Iowa and one of the fastest growing in the country. Its county seat is Adel, 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.

Iowa is a landlocked state in the upper Midwestern region of the United States. It borders the Mississippi River to the east and the Missouri River and Big Sioux River to the west; Wisconsin to the northeast, Illinois to the east and southeast, Missouri to the south, Nebraska to the west, South Dakota to the northwest, and Minnesota to the north.