15 southern Illinois counties drop in population 04/14/2017 Fifteen counties in the southernmost part of Illinois lost population from July 2015 to July 2016, fueled by significant domestic migration. TAGS: Alexander County, Franklin County, Gallatin County, Hamilton County, Hardin County, Jackson County, Massac County, outmigration, Perry County, Pope County, population, Pulaski County, Randolph County, Saline County, Union County, White County, Williamson County