A list of events that occurred on August 18 related to Six Flags.

• 1928 – Stanley McIlvaine is born.
• 2001 – Christian Family Day at Six Flags St. Louis.
• 2004 – Lightning hits a power substation near Six Flags Great Adventure, causing a power cut to the park. Twenty guests riding Batman & Robin: The Chiller were left stranded on the ride, approximately 75 feet above ground, for 40 minutes. The train's angle was such that eight of those passengers were upside-down. No injuries were reported. Only the Robin side was operating during this incident.
• 2018 – Christian Family Day at Six Flags St. Louis.