Harold Frederick Loomis (December 23, 1896 – July 5, 1976) was an American botanist and myriapodologist known for his contributions to agronomy, plant pathology, and millipede taxonomy.

He also made major contributions to the natural history of Central America and the West Indies, naming over 500 species of millipedes in total.

He worked for the U.S. Department of Agriculture from 1914 until his retirement in 1958, some 44 years, and was director of the U.S. Plant Introduction Station at Chapman Field, from 1931 to 1958.

He also collected plants and lichen from the American southwest, often contributing specimens along with botanist Robert Hibbs Peebles.

[1] The eminent myriapodologist Richard L. Hoffman wrote of Loomis: "(H)is monographs on the faunas of Hispaniola (1936) and Panama (1964) stand out as oases in a desert of chaotic short descriptive papers.