With economic activity of nearly $1.1 billion and an increase of local gross domestic product of 4.7 percent over four years, Polk County has the top performing economy in the state and the 168th in the nation, according to financial planning website SmartAsset. The SmartAsset study checked the health of local economies by their ability to capture incoming investments in business, real estate and government. Their measures were business growth, GDP growth, residential building permits and federal funding. Dallas County ranked 10th in Iowa. To play with an interactive map of the state and compare local and national results, click here.