Thomas Turpin was Thomas Jefferson's uncle by marriage. He was married to Peter Jefferson's younger sister, Mary. Thomas Turpin was one of the five executors of Peter Jefferson's estate and thus bore some degree of fiscal/material responsibility for Thomas Jefferson and his mother and siblings after Peter Jefferson died in 1757. Thomas Jefferson also lived in Thomas Turpin's house in Richmond while he was governor of Virginia; the house was located on Shockoe Hill, probably just a little south of where the governor's mansion stands, near the intersection of 12th and Franklin Streets.
There is some correspondence between Thomas Jefferson and Thomas Turpin; Jefferson also remained in touch with Thomas Turpin's sons, Horatio and Phillip, throughout their lives. What correspondence has been transcribed can be found in the Papers of Thomas Jefferson.