After graduating from the University of Arkansas, Whillock was signed by the St. Louis Cardinals prior to the 1964 season and spent five years in their farm system.
Whillock made his major league debut with Detroit on August 29, 1971, at the age of 28, following a stellar year as a relief pitcher for Double-A Montgomery, where he posted a 1.19 earned run average, five wins and 15 saves in 37 games pitched.
[1] As a Tiger, Whillock made seven relief appearances, posting an 0–2 record with a 5.63 ERA, allowing ten hits, two walks, and five earned runs in eight innings pitched.
[3] Whillock spent 1972 at Triple-A, going 6–4 with a 2.40 ERA in 45 relief appearances with the Toledo Mud Hens.
Though his time in the major leagues was short, his minor-league career lasted 11 seasons, from 1964 to 1974, Whillock went 63–76 with a 3.46 ERA, appearing in 391 games, while starting 97 of them.