| 2021 Connacnt SFC | |
| Year: | 2021 |
| Trophy: | J. J. Nestor Cup |
| Manager: | James Horan |
| Captain: | Aidan O'Shea |
| Winners: | Mayo |
| Ordinal: | 48 |
| Runnersup: | Galway |
| Runnerupcaptain: | Shane Walsh |
| Runnerupmanager: | Pádraic Joyce |
| Matches: | 4 |
| Previous: | 2020 |
| Next: | 2022 |
The 2021 Connacht Senior Football Championship was the 2021 iteration of the Connacht Senior Football Championship organised by Connacht GAA.
The 2021 Connacht championship was contested by the five counties in the Irish province of Connacht. London and New York were withdrawn from the 2020 and 2021 Connacht championships as part of the impact of the COVID-19 pandemic on Gaelic games, due to international travel restrictions. There was a full open draw for the first time in more than 40 years. It took place on 19 April 2021. Sligo withdrew from the championship in 2020 but returned in 2021. London and New York returned in 2022 but games for 2021 not expected to take place until 2026.
| Team | Colours | Sponsor | Manager | Captain | Most recent success | ||
|---|---|---|---|---|---|---|---|
| All-Ireland | Provincial | ||||||
| Galway | Maroon and white | Supermac's | Pádraic Joyce | Shane Walsh | |||
| Leitrim | Green and gold | J. P. Clarke's Saloon, New York | Terry Hyland | Wayne McKeon | |||
| London | Green and white | Michael Maher | |||||
| Mayo | Green and red | Intersport Elverys | James Horan | Aidan O'Shea | |||
| New York | Red, white and blue | ||||||
| Roscommon | Blue and yellow | Ballymore | Anthony Cunningham | Enda Smith[1] | |||
| Sligo | Black and white | AbbVie | Tony McEntee | Keelan Cawley[2] | |||
Two counties were randomly drawn to face each other in the quarter-finals. The lowest ranked county to play in the quarter-finals was Sligo of Division 4.
Three counties were given a bye to this stage and were joined by the winning team from quarter-final. The lowest ranked county to play in the semi-finals was Leitrim of Division 4.
Mayo qualified for the 2021 All-Ireland SFC semi-finals.