New census data for July 1, 2017, shows the Des Moines-West Des Moines metro area grew to 645,911, up 1.8 percent from the 2016 figure of 634,740. That gain of  11,171 residents compared to the Dallas-Fort Worth-Arlington metropolitan area’s gain of 146,238 (2 percent), the largest of any metro. Among counties, Polk County, Iowa, gained 7,062 residents, or 1.5 percent, for an estimated July 2017 population of 481,830. Dallas County added 3,050, or 3.6 percent. Maricopa County, Ariz., led U.S. county gains with 73,650, or 1.7 percent.