The Sinclair family at Islandderry were certainly a farming family. Islandderry is a townland between Dromore and Moira. James Sinclair was registered as a £10 freeholder with lands and houses at Islandderry in the Barony of Upper Iveagh on 13 May 1829.

On 3 January 1844, James Sinclair senior, James Sinclair junior and Eleanor Sinclair were accused of assaulting William Davis at Islandderry while he was seizing one heifer and two pigs under a civil bill decree. They beat him with sticks and forced him to abandon the seizure. The jury found James senior guilty of assault and the others not guilty.