sunnyside wa is in what county
Current Temperature NRÂ° Population 15,775. Sunnyside is located in Yakima County, WA. The population is 15,775, making Sunnyside the 2nd largest city in Yakima County. There are 7 public schools in Sunnyside with an average Homefacts rating of C-. The total crime rate for Sunnyside is moderate, and there are 7 registered sex offenders residing in the city.