I haven't been able to come up with "proof", but it looks like his full name may actually be William Henderson Longmire in Anderson Co, TN.
If that's the right person.
Sometimes if you google a person's name you can find family trees online with them in it. Often the creators of these trees will list their sources. Also, you may want to contact the proper authorities in Anderson Co. TN to see if you can locate a birth or death certificate.
This website looks like it could potentially be helpful as well: http://www.tn.gov/tsla/history/county/factanderson.htm
I hope you find what you're looking for.