William "Casey Bill" Weldon (December 10, 1909 – circa 1970) was an American country blues musician.
Weldon was born in Pine Bluff, Arkansas, United States, and later lived and worked in Chicago, Illinois, and was known as one of the early pioneers of the slide guitar. He played upbeat, hokum and country blues tunes. Playing a National steel guitar flat on his lap Hawaiian style, "Casey Bill" Weldon was known as the "Hawaiian Guitar Wizard". He was married to singer and guitarist Memphis Minnie in the 1920s. Only recently it has been widely accepted that Casey Bill Weldon is not the same musician as "Will Weldon" who recorded between 1927 and 1928 as a member of the Memphis Jug Band.
Weldon cut over 60 sides for Bluebird and Vocalion. He was also an active session guitarist appearing on records by Teddy Darby, Bumble Bee Slim, Peetie Wheatstraw, and Memphis Minnie. On Memphis Minnie's last recording for Bluebird Records in October 1935, Weldon accompanied her for the first time. He played on two sides, "When the Sun Goes Down, Part 2" and "Hustlin' Woman Blues." He scored solo hits with his two most well known songs, "Somebody Done Changed the Lock on That Door", and "We Gonna Move (to the Outskirts of Town)."