I found a John G. Diggs b. 1819 with wife Rachel b. 1818 in the 1850 census for Anderson Co., TN
Children: Sarah J. 11, William A. W. 10, John G. 8, George L. 6, Alfred H. 5, James R. 4, Henry C. 3, not named male 1, all born TN.
There was a John Diggs in the Henry Co., TN 1850 census, but he was born abt. 1824, the son of a Benjamin from NC, and he was single.
Check out the familysearch.org Advanced Search Record Pilot for the Diggs surname for Anderson Co., TN. There are a few entries for John Diggs and Rachel Walker's children.
In 1860, I found John G. Diggs b. 1821, in Decatur, Wise Co., TX, with Rachel b. 1818, with 11 children: William, John, George, Sarah J., Alfred, Robinson, Henry, Samuel, Mercy, Ben, and Bean? Next door is a Henry Diggs age 25, wife Elizabeth 26. (All born TN.)
Rachel was in the 1870 census in Anderson Co., with 4 children. She was alive in 1880 in Clinton, Anderson Co., TN, with son Alfred. At least 2 of her sons were alive in 1900- Alfred and Henry C. 1910 shows Henry.
There are two entries on RootsWeb showing Rachel Walker to be the 2nd wife of John W. Diggs in Henry Co. who died abt. 1880, but they are in two different counties, far apart, for each census.
There was a Henry Diggs b. 1825, in Anderson Co. who might have been a brother to John, who named a son Henry. Also a William Diggs b. abt. 1824., and a Lewis, b. abt. 1822.
Hope this is of some help to you!