Before any major housing development occurred in Sunnyside, the area west of Pecos Street was occupied by small truck farms, orchards and undeveloped land. In 1879, the northeast corner of the neighborhood was incorporated as the town of Argo. As a “company town,” Argo was settled primarily by Swedes who worked at the smelter and by others who worked for the Moffatt Railroad.

Sunnyside became a part of Denver through three annexations. The first two occurred under the Colorado Session Laws of 1883 and 1889. The third took place when the town of Argo was dissolved and merged with Denver in 1902. As a result, the housing in Sunnyside is a mix of many types, ages and style of architecture. Most of the oldest housing is found east of Pecos Street.

During the 1940s, the northern portion of Sunnyside was occupied by “Quonset Town”. The Quonset huts, prefabricated shelters made of corrugated metal shaped like a half-cylinder resting on its side, were built by the U.S. Department of Defense to alleviate the housing shortage experienced after World War II. After the Quonset huts were demolished, this area remained vacant for many years.

Since the 1950s. Sunnyside has been undergoing a period of change. The Quigg Newton Homes, now Denver’s largest public housing project, was built during the 50s. Some industrial encroachment has occurred as well, along the area’s eastern flank.

In the mid-1960s, Interstate 70 was built along the northern edge of Sunnyside, isolating the Chaffee Park and Regis neighborhoods from the rest of northwest Denver.