Corridor Business Journal: Dallas County residents have the most purchasing power in Iowa, according to a new study by SmartAsset. The study compared median household income and cost of living data to find the counties where residents have the most purchasing power. Dallas County residents led the state in purchasing power, with a high median income of $82,719 and a cost of living of $49,092. The results gave Dallas County a purchasing power index of 74.32, far ahead of No. 2 Sioux County, which had a purchasing power index of 67.73. Rounding out the top five were Warren, Delaware and Polk counties.