Samuel couldn't have been born in DeKalb County because it was established Dec 2, 1837 from Warren, Cannon and White counties. I'd look in those counties for his and Sintha's early records.
1870 DeKalb Co. TN
Samuel Barger, b. TN, 69, farmer
Sintha, b. GA, 65
Martha, b. TN, 35
Sintha E., b. TN, 25
1880 DeKalb Co. TN
Lemuel Barger, b. TN, 50, single, farmer
Cynthia, ma, b. GA, 74, widow, rheumatism
Martha Evans, sister, b. TN, 48, widow
Nance E. neice, b. IL, 16
Sinthy David Barger
Born: 20 Sept 1805
Died: 26 Feb 1881
Buried: Salem Baptist Church Cemetery, Liberty, DeKalb, TN
The DeKalb County Archives
1 Public Square
Smithville 37166 or eamil email@example.com
may have more information.
I'd contact the Justin Potter Library, http://dekalblibraries.net/
and ask if they have newspaper death notices for Samuel and Sinthy. Successful Searching!