Henry Warner Slocum, Jr. (May 28, 1862 – January 22, 1949) was an American male tennis player who was active in the late 19th century.

[3] Slocum graduated from Yale University in 1883 and started playing tennis in 1884 although he entered few prominent tournaments until the spring of 1886.

[4] Slocum won the 1888 Men's Singles title at the U.S. National Championships' in Newport against defending champion and compatriot Howard Taylor in straight sets.

The next year he successfully defended his title in the Challenge Round with a victory over Quincy Shaw.

He was president of the United States National Lawn Tennis Association (USNLTA) in 1892 and 1893.