Susan,

The following William Cox are those that received Confederate pensions in Texas. You might get lucky.
I would check these and see if you find a connection. It is not very expensive to order copies and they often contain lots of good info.

http://www.tsl.state.tx.us/arc/pensions/index.html

Cox, Susan 39953 Ellis Cox, William 27118
Cox, William 27118 Comanche
Cox, William Thomas 13794 Falls

Good Luck,
Sherry Bob