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.

Polk County is located in the U.S. state of Iowa. As of the 2020 census, the population was 492,401. It is Iowa's most populous county, and home to over 15% of the state's residents. The county seat is Des Moines, which is also the capital city of Iowa. Polk County is included in the Des Moines–West Des Moines, IA Metropolitan Statistical Area.