Lookup his find-a-grave memorial in Eastland County. Also, there are User Submitted Genealogies viewable on https://familysearch.org/
Logon to website then click "Search". Click "Any" under subheading "Search with a life event". Enter Tarrant TX in the "Any Place" box. Click highlighted "Parents" then enter William B Johnson and Sophia in the appropriate boxes. Click "Search" then scroll to bottom of page for user submitted genealogies.