Several tribes in the region were relocated onto the Yakama Indian Reservation following the 1855 signing of a treaty with the federal government.

Granger was involved in the financing and construction of the Sunnyside Canal which would have allowed 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.

The site contained "1 bank, 11 stores, 3 hotels, 1 newspaper [the Sunnyside Sun, still publishing in 2020], 2 blacksmith shops, 2 livery barns, 3 churches, and a large and growing school".

[8] 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.

[9] The Dunkards, members of the German Baptist Progressive Brethren, relocated to Sunnyside in order to form what they called the Christian Cooperative Colony.

They enforced clauses prohibiting alcohol, dancing and gambling as a condition on every parcel of land sold.

[8] Under the leadership of mayor William Bright "Billy" Cloud (1870–1959), Sunnyside initiated a project to pave its dirt streets on June 5, 1917.

This project was necessary since years of irrigation had raised the water table to the point that the streets had become unbearably muddy.

The city manager, however, is directly accountable to and can be removed by a majority vote of the council at any time.

[12] According to the United States Census Bureau, the city has a total area of 6.63 square miles (17.17 km2), all of it land.

[13] Sunnyside lies approximately 180 miles away from Seattle to the west, Spokane to the east and Portland to the southwest.

[19] Usually taking place in early December, the parade includes "farm implements: combines, boom trucks, sprayers, swathers, grape pickers, and all types of tractors" decorated with colorful lights.

The Darigold Dairy Fair manufactured 150 million pounds of cheese annually[22] but was mostly noted for its colorful facade and circus-like decorations, which included a pair of cows swinging on a flying trapeze.

[24] Located downtown, the museum houses and displays artifacts and documents with a focus on daily life in Sunnyside during its early years.

The Sunnyside Memorial Cemetery, founded by the Ball Family, is located north of town.

Erected in 1927, it is a two-story structure with an adjacent gymnasium attached to the east wing of the building.