She is married to Unknown Jones.
They got married
She is probably not the Nancy Brown that married a Thomas Jones in 1811 (bondsman John Brown).
First, Polley is not a nickname for Nancy (it is a nickname for Mary). Her mother's name was Mary on the 1850 census and nickname Molley in her husband's will in 1830. It would make sense that if mother and daughter were both named Mary that they would have different nicknames for Mary (Molley and Polley).
Second, the above Thomas Jones could be Thomas J. Jones, brother of Burrel Jones [Burrel married Elizabeth, sister of this Polly]. That Thomas apparently had a marriage prior to his marriage to Sarah Matlocks, but that would mean that the first wife would not be alive in 1830 to be included in John Brown's will. It is possible that Nancy was a sister to Polley and died before the father made his will (but why would he not name Thomas J. Jones eldest son - a son from a marriage prior to Sarah Matlocks - if Nancy was his daughter that had died? I have not been able to trace the Polley named in John Brown's will.
External link: https://www.WikiTree.com/wiki/Brown-48306
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