Membership in the organization is decided through an audition process and is open to all music students in Central Illinois.
Students through grade 12 are eligible for membership in the Youth Symphony, Jazz Orchestra, Concert Orchestra, Preparatory Orchestra, and various ensembles. Entrance auditions are held every Spring for admittance into Youth Music Illinois for the following season. Entrance auditions will also be held the following August prior to season start, to fill any openings still available. Finally, Youth Music Illinois will hold auditions again in the late Fall or over winter break, prior to the first rehearsal of the Spring semester.