William Thomas Walthall has extensive coverage in "Find-a-grave." Born 2 June 1820 (Virginia), died 20 May 1899 (Vicksburg), mainly associated with Alabama. There is not, however, an indication where he was buried, though if the funeral was in Vicksburg, I'd assume he was buried there, somewhere. This information on Find-A-Grave was provided by Eugene R. Walthall, presumably a descendant, whose contact information can be found there.