Thomas had his bouts of ill health. In fact in 1667, when he was laid low with the gout, he was never expected to recover - though he did. And in any case he managed to outlive all his male relatives, both his own and the succeeding generation, leaving him sadly without any grandsons from male issue. Family legend has it that he was twice offered an earldom during his final years. Yet without there being any male heir from his own loins, and with the inheritance of Longleat required by family entail to pass through the male line of descent from Sir John Thynne, he didn't really feel there was much point in accumulating any additional honours. He was more inclined to suppose that the whole line would soon be extinct, or too distant in blood ties for him to trouble himself. He had four sons, including Henry Thynne (1675–1708), all of whom predeceased him. He has an extensive article in the "Dictionary of National Biography".