...S&P Global Ratings assigned its '###' long-term rating to Polk County, Iowa's series 2017C general obligation (GO) refunding bonds. The outlook is stable. The county's full-faith and credit pledge, and an agreement to levy ad valorem property taxes without limitation on the rate or amount, secure the bonds. The series 2017C bond proceeds will be used to current refund the county's outstanding series 2012C for interest cost savings. Polk County's bonds are eligible to be rated above the sovereign because we believe the county can maintain better credit characteristics than the U.S. in a stress scenario. Under our criteria, U.S. state and local governments are considered to have moderate sensitivity to country risk. (For more information, see "Ratings Above The Sovereign--Corporate And Government Ratings: Methodology And Assumptions," published Nov. 19, 2013 on RatingsDirect.) The county's local property tax revenues are the primary source of security on the bonds, which significantly limits...