The population of Marion County has increased slightly, according to estimates released by the US Census Bureau. The period covered in the estimate was from April 1, 2010 to July 1, 2011. During that time the population increase in Marion County was .1%. The total population for Marion County is estimated to be 33,335. Dallas County west of Des Moines showed a growth rate of 5%, the seventh fastest county growth rate in the country. Of our surrounding counties, Polk, Warren, Monroe and Mahaska counties showed slight increases in population numbers, with Lucas and Jasper showing slight decreases.