Iowa’s fastest growing counties are blossoming because of their suburbs. The latest Census data shows Dallas County’s population grew 37 percent in the past decade. Dallas County is just to the west of Polk County and Des Moines. The state’s second-fastest growing county was Johnson, which is home to the University of Iowa. Polk County was third and Linn County — home to the Cedar Rapids/Marion metro — was the fourth-fastest growing county in the decade. Fifty-four counties had more people in 2000 than they did in 1990 but 45 counties lost population.