1984 All-Ireland Under-21 Football Championship
| Championship details | |
|---|---|
| All-Ireland Champions | |
| Winning team | Cork (5th win) |
| Captain | Niall Cahalane |
| All-Ireland Finalists | |
| Losing team | Mayo |
| Provincial Champions | |
| Munster | Cork |
| Leinster | Dublin |
| Ulster | Down |
| Connacht | Mayo |
The 1984 All-Ireland Under-21 Football Championship was the 21st staging of the All-Ireland Under-21 Football Championship since its establishment by the Gaelic Athletic Association in 1964.
Mayo entered the championship as defending champions.
On 26 August 1984, Cork won the championship following a 0–9 to 0–6 defeat of Mayo in the All-Ireland final. This was their fifth All-Ireland title overall and their first in three championship seasons.