Jackie Stewart, the Comanche development director, said the blast occurred on the Comanche High School softball field. That was the site for the display, Family on the Fourth, sponsored by the local Kiwanis Club.
The identity of the person killed had not been released Thursday afternoon.
"There was an explosion, a trailer and vehicles caught on fire," Stewart said. "Four individuals were injured, three of those critically."
Fire Lt. Marcus Nettleton said investigators were still trying to determine what triggered the explosion.
Comanche is a town of about 4,000 in central Texas.