As of yesterday nearly two thirds of Polk County residents had returned their 2010 Census forms, saving the federal government the time and expense of sending someone to their home to gather information. According to the Census Bureau, every percentage point increase in the national participation rate by mail saves about $85 million. Households have until mid-April to mail back their forms before census takers begin going door to door to residences that failed to respond. Polk’s mail return rate so far tops the national and state return rates of 60 and 62 percent, respectively.