1984 All-Ireland Under-21 Football Championship#Munster Under-21 Football Championship

{{short description|Gaelic football competition}}

{{Use dmy dates|date=April 2022}}

{{infobox

|title = 1984 All-Ireland Under-21 Football Championship

| image =

|bodyclass=vevent

|headerstyle = background:#BFD7FF;

|labelstyle=white-space: nowrap

|datastyle=white-space: nowrap

|header1=Championship details

|label2=Dates

|data2=

|label3=Teams

|data3=

|header4=All-Ireland Champions

|label5=Winning team

|data5=Cork (5th win)

|label6=Captain

|data6=Niall Cahalane

|label7=Manager

|data7=

|header8=All-Ireland Finalists

|label9=Losing team

|data9=Mayo

|label10=Captain

|data10=

|label11=Manager

|data11=

|header12=Provincial Champions

|label13=Munster

|data13=Cork

|label14=Leinster

|data14=Dublin

|label15=Ulster

|data15=Down

|label16=Connacht

|data16=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.{{cite news|url=https://www.balls.ie/gaa/greatest-u21-gaelic-football-team-time-vote-250003|title=Which Is The Greatest U21 Gaelic Football Team Of All Time?|publisher=balls.ie|accessdate=15 July 2017|date=10 March 2015}} This was their fifth All-Ireland title overall and their first in three championship seasons.