Walled by the Horse Heaven Hills and surrounded by valleys checkered with farms and orchards. This arid region attracted the attention of land promoters in 1893. Walter N. Granger, president of the newly formed Sunnyside Canal Company, named the town in 1893 and opened the first store in January 1894. By the middle of that year the town was given a post office, and a stage connected it with Mabton.
Aiding in the development of the town was the Christian Co-operative Movement, sponsored by a branch of the Dunkard Church, and organized under the leadership of S. J. Harrison, Christian Rowland, and H. M. Lichty in 1898. The co-operatives made a large settlement and, in 1901, established their own telephone system; the next year a bank was formed, and an election for incorporation was held.
Several years earlier, the Sunnyside Canal Company, headed by Walter N. Granger, had purchased much of the land in the region and had begun its reclamation by irrigation. The Sunnyside Land and Investment Company was founded in the early 1900s. The town was chartered in 1904, the same year the Northern Pacific Railway extended its lines into the town. In 1905, the United States Reclamation Service took over the Sunnyside Irrigation Project, one of the first in the state.
Most of the early inhabitants were farmers who were attracted by the religious basis of the new community, as well as by the agricultural possibilities of the irrigated region. Many families came here fleeing the drought in the mid-west United States. As of 1941, 75 other families had come to Sunnyside from the same district in South Dakota as did the original co-operative colony. The influx of drought victims created difficult housing situations; in some cases two families were crowded into one small cabin, barely large enough for two persons. Today the importance of this agricultural heritage manifests in one of the nation’s most notable parades, the Lighted Farm Implement Parade, held the first Saturday in December.
Asparagus and tomatoes were the most important products grown on the rich soil of the irrigated farm plots that surround Sunnyside. There are also vineyards, orchards, and dairy farms in the vicinity. Several wineries, and agriculture-based industries are among the major economic assets of the town. The 1930s era Roza Irrigation Development gave added impetus to agricultural enterprises in the valley.
An annual event was the Sunnyside Fete Day; high points of the fete were the flower show, soap-box derby, gas-model airplane contest, night pageant, and street dance carnival. Today this festival is no longer held, though the current Old-Fashioned Fourth of July Festival features similar events.
For a time known as the “Holy City,” Sunnyside had 22 churches. The major religious denomination is the Zionist. The city’s charter provides that no saloon is to be maintained and no hard liquor is to be sold within the city limits, and the State Liquor Store is located beyond the boundary line. Paradoxically, Sunnyside taverns once sold some of the largest 10c glasses of beer in the state. Today hard liquor is sold within the city limits.