Sunnyside is a city in Yakima County, Washington, United States. The population was 16,375 at the 2020 census, making it the second-most populous city in Yakima County. The modern settlement of Sunnyside was founded by Walter Granger in 1893. The name was coined by a merchant named W. H. Cline.
Sunnyside's population increase at this time was stimulated by the immigration of the Dunkards from South Dakota who were moving to the town. The Dunkards, members of the German Baptist Progressive Brethren, relocated to Sunnyside in order to form what they called the Christian Cooperative Colony.
Located in the heart of the Yakima Valley, Sunnyside is surrounded by sweeping vineyards, lush hop fields, and farm country. Sunnyside takes pride in its farming heritage. World-renowned wine regions are just minutes in every direction. A diverse and growing city, Sunnyside boasts a diverse array of dining, lodging, shopping and cultural attractions and events.