Keith - Just a quick search, and found one Charles William McKinney who was born about 1884, died on 11 April 1965 in Red Bay, Franklin Co., Alabama. Record states spouse's name as "Clemmie" McKinney, father's name of "Dock McKinney" and mother's name as "Rebecca Hodge". Record was with LDS site, film # 1909077, reference # 8654. Checked 1880 Census for Colbert Co. it shows the following:
Rock Creek, Colbert Co. Alabama Dock McKinney born: 1854 Alabama// Rebeca McKinney born 1856 Alabama/NC/NC Nancy McKinney born 1876 Alabama/Alabama/Alabama Sally McKinney born July 1879 Alabama/Alabama/Alabama
Checked 1900 Census for Allsboro, Colbert Co., Alabama, it shows the following:
Dock McKinney born March 1850 Alabama/UNK/UNK Beckie McKinney born Sept. 1853 Alabama/NC/NC Charlie McKinney born March 1883 Alabama/Alabama/Alabama Wesley McKinney born July 1887 Alabama/Alabama/Alabama Susie McKinney born Sept. 1889 Alabama/Alabama/Alabama Docke McKinney born Sept. 1894 Alabama/Alabama/Alabama
Based on these two census I think you can rule out him being adopted and your next search should be on who was Dock's parents.