William Temple Hornaday, Jr. (born December 1, 1854 near Plainfield, Indiana; died March 6, 1937 in Stamford, Connecticut) was a biologist.

He was the son of William Temple Hornaday, Sr., and Martha Hornaday.

Hornaday joined expeditions to Cuba and Florida (1874-1875), the West Indies and South America (1876), and Europe, Egypt, Arabia, India, Ceylon, Malay, Borneo (1876-1879).

In 1880, he started the National society of American taxidermists.

In 1882, he became chief taxidermist of the United States National Museum in Washington, D.C.