Cromwell replaces Charlie Baggett, who left St. Louis after one season to become assistant head coach and wide receivers coach at the University of Tennessee.
Said Cromwell, whose entire NFL playing career (1977-87) came with the Rams when they were located in Los Angeles: "I am excited to be back with the Rams family. I appreciate Coach Spagnuolo for giving me this opportunity, and I look forward to working with the receivers on our roster and the coaching staff."
Cromwell spent the past two seasons as offensive coordinator at Texas A&M. Before that, he coached wide receivers with the Seattle Seahawks from 1999 to 2007.
The Associated Press contributed to this report.