Both Leinster U21FC semi-finals will be played at neutral venues on Wednesday 18 March.
Defending provincial and All-Ireland champions Dublin will face Longford in Navan.
In the other semi-final Meath will meet the winners of tonight's remaining quarter-final between Kildare and Offaly, in Portlaoise.
Wednesday 18 March
Longford v Dublin, Pairc Tailteann, Navan, 7.30pm
Meath v Offaly or Kildare, O'Moore Park, Portlaoise, 7.30pm
Extra time if necessary must be played if sides finish level.