The 69 full-time workers and 50 part-time workers at the plant were told of the decision at a meeting last week.
The company, which makes security electronic devices, was formerly Tyco Electronics.
Its wireless division, including the Cork operation, was taken over by Harris in May.
In a statement, Harris says that following a review carried out locally the decision to phase out operations and close the Little Island plant next June, has been taken.
A redundancy package, which has been described as generous, has been agreed.
The US multi-national said the decision was taken because of existing capabilities elsewhere in the company.