Two men, aged 22 and 29, and a 38-year-old woman are currently in custody.
A 26-year-old man remains in critical condition after being seriously injured in an attack in The Height area of the town.
The Height is an area at the junction of O'Connell Street, Abbey Street and Bank Place.
Gardaí believe the victim was walking in the company of friends when he was set upon by another group.
He was taken to the Mid Western Region Hospital Limerick with what is understood to be a head injury.
Gardaí have issued an appeal for witnesses.
