| 1891 U.S. National Championships | |
|---|---|
| Date | August 22 - August 31 (M) June 23 - June 27 (W) | 
| Edition | 11th | 
| Category | Grand Slam | 
| Surface | Grass | 
| Location | Newport, R.I., United States (M) Philadelphia, PA, United States (W) | 
| Champions | |
| Men's singles | |
|  Oliver Campbell[1] | |
| Women's singles | |
|  Mabel Cahill[1] | |
| Men's doubles | |
|  Oliver Campbell /  Bob Huntington | |
| Women's doubles | |
|  Mabel Cahill /  Emma Leavitt Morgan | |
List of champions of the 1891 U.S. National Championships (now known as the US Open). The men's tournament was held from August 22 to August 31 on the outdoor grass courts at the Newport Casino in Newport, Rhode Island. The women's tournament was held from June 23 to June 27 on the outdoor grass courts at the Philadelphia Cricket Club in Philadelphia, Pennsylvania. It was the 11th U.S. National Championships and the second Grand Slam tournament of the year.:[1]
Finals
Men's singles
 Oliver Campbell defeated
 Oliver Campbell defeated  Clarence Hobart  2–6, 7–5, 7–9, 6–1, 6–2
 Clarence Hobart  2–6, 7–5, 7–9, 6–1, 6–2
Women's singles
 Mabel Cahill defeated
 Mabel Cahill defeated  Ellen Roosevelt  6–4, 6–1, 4–6, 6–3
 Ellen Roosevelt  6–4, 6–1, 4–6, 6–3
Men's doubles
 Oliver Campbell /
 Oliver Campbell /  Bob Huntington defeated
 Bob Huntington defeated  Valentine Hall /
 Valentine Hall /  Clarence Hobart 6–3, 6–4, 8–6
 Clarence Hobart 6–3, 6–4, 8–6
Women's doubles
 Mabel Cahill /
 Mabel Cahill /  Emma Leavitt Morgan defeated
 Emma Leavitt Morgan defeated  Grace Roosevelt /
 Grace Roosevelt /  Ellen Roosevelt 2–6, 8–6, 6–4
 Ellen Roosevelt 2–6, 8–6, 6–4
Mixed doubles
 Mabel Cahill / Wright defeated
 Mabel Cahill / Wright defeated  Grace Roosevelt / Lee  6–4, 6–0, 7–5 †
 Grace Roosevelt / Lee  6–4, 6–0, 7–5 †
† - The Mixed Doubles event was not an official event in 1891