T.F. Johnson received the first grant for Rock Island. It was subsequently owned by Dr, Mercer and eventually owned by Thomas Laughlin. In the 1860’s the island was obtained by the Government and was used as a quarantine depot for first class passengers who may have entered Trinidad waters with infectious diseases. These elite passengers would be detained on the island and a yellow flag would then be hoisted to inform that an infected individual was present on the island and interaction with the island was temporarily not allowed. The individual would remain on the island until the disease had vacated its host. Rock island is under the protection of the National Trust of Trinidad and Tobago as a heritage site.