Mercer County, Pennsylvania (PA) County population in 2014: 114,884 (56% urban, 44% rural); it was 120,293 in 2000. County owner-occupied with a mortgage or a loan houses and condos in 2010: 19,319. County owner-occupied free and clear houses and condos in 2010: 14,619. County owner-occupied houses and condos in 2000: 35,613.