The other way to pursue this search would be to check Texas pension applications. I don't see any possibility in Grayson County, but several others applied from other counties:

Williams, C. J. (Mrs), Ellis County, veteran = Williams, John B.
Williams, John Benjamin, McLennan County
Williams, Kate J., McLennan County, veteran = Williams, John Benjamin
Williams, Martha Elizabeth, Lampasas County, veteran = Williams, John Barnet

Contact me at cssoldier@hotmail.com if I can assist you further with this.