Sunnyside is a city in Yakima County, Washington, United States. As of the 2010 census the population was 15,858.HistoryOn September 16, 1902, residents voted 42 to one to incorporate as the town of Sunnyside. By state law a town needed to have 300 citizens in order to legally incorporate. With 314 residents, Sunnyside was just eligible to legally vote for incorporation.The first mayor of Sunnyside was the town druggist James Henderson.The settlement was founded by Walter Granger in 1893. The name "Sunnyside" was coined by a merchant named W. H. Cline. Granger was involved in the financing and construction of the Sunnyside Canal which would allow Yakima River water to irrigate the area. However, due to the Panic of 1893, Granger's creditors foreclosed on the canal, and the town's population dwindled to seven families. However, by the end of 1901, the population had doubled, finally exceeding 300 people. The townsite contained "1 bank, 11 stores, 3 hotels, 1 newspaper, 2 blacksmith shops, 2 livery barns, 3 churches, and a large and growing school."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 population of Dunkards was of such notable size that by 1902 it was noted that they had "built a commodious place of worship at Sunnyside" which was the largest church in Yakima County at the time.The Dunkards, members of the German Baptist Progressive Brethren, relocated to Sunnyside in order to form what they called the Christian Cooperative Colony. The Brethren bought the entire town site and were the developers of its first bank, and a telephone system. They enforced clauses prohibiting alcohol, dancing, and gambling as a condition on every parcel of land sold. Because of this, old maps of Washington identify the town with a cross or halo symbol.
