| Tournament details | |
|---|---|
| County | Down |
| Province | Ulster |
| Year | 2021 |
| Trophy | Frank O'Hare Cup |
| Sponsor | Morgan Fuels |
| Teams | 16 |
| Defending champions | Kilcoo |
| Winners | |
| Champions | Kilcoo (19th title) |
| Qualify for | 2021 Ulster Club SFC |
| Runners-up | |
| Runners-up | St Mary's Burren |
The 2021 Down Senior Football Championship was the 113th official edition of Down GAA's premier Gaelic Football tournament for senior clubs in County Down. 16 teams competed with the winner representing Down in the Ulster Senior Club Football Championship. The tournament operated a double elimination format for the opening two rounds of the championship, with the winners and early round losers rejoining at the quarter final stage.
Kilcoo were the holders after defeating Carryduff in the 2020 final, and retained the title following their victory in the 2021 final against St Mary's Burren.