Roberts, Gary Boyd; Ancestors of American Presidents. Boston: New England Historic Genealogical Society, 2009.
Jacobus, Donald Lines. A History of the Seymour Family: Descendants of Richard Seymour of Hartford, Connecticut for Six Generations. Compiled and arranged for publication under the direction of George Dudley Seymour (New Haven, Connecticut: 1939), p. 46, 62, 63.
Jacobus, Donald Lines. History and Genealogy of the Families of Old Fairfield (New Haven, Connecticut: Tuttle, Morehouse & Taylor Co., 1930-1932), vol. 1 p. 538.
It may be possible to confirm family relationships with Thomas by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree:
Denny Seymour :
Family Tree DNA Y-DNA Test 111 markers, haplogroup R-BY3298, FTDNA kit #108347 +
Y-Chromosome Test 419 markers, haplogroup R-Y20344