I could not find any information on Grady Kidd Mathis. However, I did find that Thelma Kidd, her sister, was the daughter of Alex Walter Kidd. I'm assuming that Grady was born after Thelma. I found Thelma and her parents in the 1930 Alex W. Kidd was born 28 Feb. 1894 in Kanawha Co., WV, and died in Charleston, Kanawha Co., WV on 8 Nov. 1950. His death certificate is online at the West Virginia Archives, http://www.wvculture.org/vrr/va_select.aspx

So I would start my search in Kanawha County. You should try to locate a copy of the obituary for the father, Alex W. Kidd, which might give you the names and locations at that time of his children. Good luck!