It was located following a search of a residence in Aughnacliffe yesterday afternoon.
Officers attached to the Roscommon/Longford Divisional Drugs Unit discovered the growhouse in two bedrooms and the basement area of the property.
Cannabis plants worth 45,000 euro were seized, along with 85,000 euro worth of cannabis herb.
A man in his 30s was arrested at the scene - he's since been charged and is due before Mullingar District Court this afternoon.
