A "privileged" list owner can define if the list membership is visible to: public, members only, or owner only.

1. Log into https://lists.illinois.edu.
2. Select your list from the menu on the left.
3. Click "Admin" from the menu on the left.
4. Click on "Edit List Config."
5. Click on "Privileges."
6. Select the desired option from the section, "Who can review subscribers."
• no one can review (closed)
• restricted to subscribers or local domain users (intranet)
• listmaster only (listmaster)
• only owner (and listmaster) (owner) 
• restricted to subscribers (default value)
• anyone (public)
7. Click on "Apply modifications," which is located at the bottom of the page.