| Champ: |  Robin Montgomery |
| Runner: |  Kristina Dmitruk |
| Score: | 6–2, 6–4 |
| Before Year: | 2019 |
See main article: 2021 US Open (tennis).
Camila Osorio was the defending champion, having won the previous edition in 2019, but was no longer eligible to participate in junior events. She participated in the women's singles event, but lost to Ons Jabeur in the second round.
Robin Montgomery won the title, defeating Kristina Dmitruk in the final, 6–2, 6–4.
All seeds received a bye into the second round.