As per the Indiana State Fairgrounds website;

The Indiana State Fairgrounds & Event Center follows the Indiana Department of Health and Center for Disease Control and Prevention’s (CDC’s) guidance on COVID-19 protocols for the State of Indiana. Masks will not be required while visiting the Indiana State Fairgrounds & Event Center for fully vaccinated individuals in public outdoor settings. If you are not vaccinated, guests are encouraged to wear a face covering and should follow the CDC guidelines on when wearing a face covering is warranted. The CDC currently recommends fully and non-vaccinated individuals wear a mask in public indoor settings

So recommended but not mandatory.