List of champions of the 1909 U.S. National Championships tennis tournament (now known as the US Open). The men's tournament was held from August 17 to August 27 on the outdoor grass courts at the Newport Casino in Newport, Rhode Island. The women's tournament was held from June 21 to June 27 on the outdoor grass courts at the Philadelphia Cricket Club in Philadelphia, Pennsylvania. It was the 29th U.S. National Championships and the second Grand Slam tournament of the three played that year.
See main article: 1909 U.S. National Championships – Men's singles. 
William Larned (USA) defeated William Clothier (USA) 6–1, 6–2, 5–7, 1–6, 6–1
See main article: 1909 U.S. National Championships – Women's singles. Hazel Hotchkiss (USA) defeated Maud Barger-Wallach (USA) 6–0, 6–1
Fred Alexander (USA) / Harold Hackett (USA) defeated Maurice McLoughlin (USA) / George Janes (USA) 6–4, 6–4, 6–0
Hazel Hotchkiss (USA) / Edith Rotch (USA) defeated Dorothy Green (USA) / 
Lois Moyes (CAN) 6–1, 6–1
Hazel Hotchkiss (USA) / Wallace F. Johnson (USA) defeated Louise Hammond Raymond (USA) / Raymond Little (USA) 6–2, 6–0