Originally drafted by the Dodgers in the 20th round of the 2008 draft, Cox elected to attend the University of Arkansas rather than sign. After a sophomore season that saw him set schools records in hits (102) and batting average (.429), St. Louis selected him in the first round, 25th overall, in 2010. In his first full year in the minors, Cox batted .306 with 13 home runs and 68 RBIs between High-A Palm Beach and Double-A Springfield. He reached Triple-A Memphis in 2012, and was then traded to the Miami Marlins in exchange for Major League reliever Edward Mujica. Cox was then with the Marlins organization until this past offseason when he was selected by the Washington Nationals in the Triple-A phase of the Rule 5 draft. He was with Washington during spring training but was released in April, allowing him to sign with the Wingnuts.