The case is an Aitutaki resident, and the person is isolating at home.
Household contacts are currently being identified and are asked to quarantine.
Like Rarotonga, the population on Aitutaki is highly vaccinated and Prime Minister Mark Brown said they are prepared for this.
Over the weekend 24 new cases were confirmed, bringing the total number to 130.
R-A-T tests will be used to diagnose new cases in the Cook Islands as is occurring in New Zealand.
No additional PCR test will be required except for clinical reasons.