The owners of commercial, industrial and railroad properties in Polk County received $18.6 million in credits against their properties this year, the Polk County assessor’s office said. The credits were part of legislation enacted in 2013 that also reduced the assessed value of commercial properties to 90 percent of full value and reclassified apartment buildings as residences, which will result in a nearly 50 percent reduction in their value for property tax purposes. In Polk County, 8,980 parcels received an average credit of $2,070. The maximum tax credits was $4,380.