Platt has led the orchestra since 1993. He is also conductor in residence at Chicago Opera Theater and music director of the Waukesha (Wisconsin) Symphony and the Marion (Indiana) Symphony.
"On behalf of the board, musicians, and community of Racine, I wish to thank Alexander for his leadership, dedication, and professionalism," Racine Symphony president Joseph Veranth said in a statement. "The quality of performances under his tenure rose to a level far above what anyone could have expected."
The orchestra is accepting applications for the music director position through August 15.