Ticket sales for events. All state championship series events, including those hosted at schools that charge admission have a portion go to the IHSA.
TV rights.
Radio rights.
Photography rights.
Merchandise sales.
hosting fees for events - the state basketball championship bid process called for the winning city to pay the IHSA for the right to host the event. Most state championships don’t have these.
Fees paid by vendors to sell at events.
Fees charged to officials for licensing
You can access their 990 to see. The IHSA is a 501c3. Only 368000 of 10.8 million in revenue is contributions.
Tournament revenue from all sources is 75% of their revenue and I think this includes hosting fees, tickets and merchandise at the events.