During National Forestry Week in 1928, the Forestry Committee of the Chamber of Commerce convinced the City Council to establish an arboretum in Washington Park to preserve evergreens for educational and recreational purposes. Multnomah County gave the Parks Bureau perpetual use of approximately 145 acres of land north of Washington Park for this purpose. It was named Hoyt Arboretum in honor of Ralph Warren Hoyt, the county commissioner who championed the formation of the arboretum.
Most of the collection is arranged in family groups: all the oaks are in one area and all of the redwoods are in another. Grouping by scientific classification, or taxonomic arrangement, was in vogue when the Arboretum was first laid out. In the 1930s, planners decided to use Fairview Boulevard to divide the conifers from the deciduous trees: conifers were planted on the west side and deciduous trees on the east.
Although Hoyt Arboretum is relatively young, it possesses the largest group of distinct species of any arboretum in the U.S. Its plant collection contains 10,000 individual trees and shrubs, representing nearly 1,000 different species from around the world.