A list of events that occurred on September 21 related to Six Flags.

• 2013 – Gary Story dies.
• 2018 – Fright Fest 2018 begins at Six Flags Discovery Kingdom.
• 2019
  • Fright Fest 2019 begins at Six Flags America.
  • Fright Fest 2019 begins at Six Flags New England.
  • Fright Fest 2019 begins at Six Flags Over Georgia.
  • Fright Fest 2019 begins at Six Flags Over Texas.