Many of the Turnbow's were in Adair County KY prior to moving to Maury County. There was a Samuel Turnbow who got a land grant of 150 acres in Adair County in 1824.
Jeremiah Turnbow shows up in McNairy County in 1830, living very near to Elisha S. Powell, my ancestor. Elisha lived in Maury & Giles County circa 1809-1817, and lived very near the Turnbow's. Elisha's Powell kin came to Maury County from Adair County KY.
I have studied the Maury tax rolls a great deal. Some early ones are published. You can also get microfilm rolls by interlibrary loan from the TN State Archives.