It probably was Washington, Maine, Knox County. There were several by the name of Thomas Johnston, a common first name in the family. Thomas Johnston, Esq. settled near Bremen/Bristol in 1759. Born in Scotland 1735 and died 1811. One of his sons by his second wife, Anna Sprowl, was Thomas, born 1768. Your on your own from there. My family descended from Thomas'(1768) brother James (1775-1824).