The drug seizure was said to be worth over €256,000.
Gardaí in Carrickmacross, Monaghan discovered a grow house at a residential premises on Coolshannagh Road on Saturday, 1 December.
During the course of the search, Gardaí discovered what is being described as a "sophisticated grow house".
The grow house is said to have had over 320 cannabis plants at a mature stage of growth.
The plants have an estimated street value of €256,000.
Gardaí said that the premises was sealed off for a forensic technical examination. While no arrests have been made and investigations are continuing.
Images of the grow house can be seen below:
