Eight hundred of the plants, as well as electrical equipment, were seized at a workshop in Millisle on Friday.
Police said it was one of the biggest and most sophisticated production operations they had uncovered recently.
Insp Andy Dunlop said there were "young plants, the remnants of a previous harvest, space for drying the product and space for waste products".
He added: "No arrests were made this morning but our enquiries will be continuing over the coming days."
Cannabis plants worth an estimated £400,000 have been seized by police  in County Down.