The 1880 US census, Guadalupe county, Texas indicates your ancestor, [https://www.wikitree.com/wiki/Williams-39096
] Richard Sinclair Williams, and wife, Nancy Jane (Collins) Williams were living in Guadalupe county with their 8 children: Three of the children were born in Alabama, with son, Jonathan born in Texas. Could he be your your Dr John Williams ? Richard had a brother named Thomas also found in the 1880 Guadalupe county, Texas US Census. He had no children named John in his household.
"United States Census, 1880," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MFNF-2ZD
: 15 July 2017), Richard Williams, Precinct 2, Guadalupe, Texas, United States; citing enumeration district ED 73, sheet 248A, NARA microfilm publication T9 (Washington D.C.: National Archives and Records Administration, n.d.), roll 1308; FHL microfilm 1,255,308.