All were on the boardwalk or on walkways around Old Faithful Geyser when a small thunderstorm cell produced a single lightning bolt.
Park staff immediately converged on the scene of the strike and began to triage the injured.
Two people were on the asphalt walkway between the Old Faithful Lodge and the boardwalk which circles the geyser.
Bystanders had started CPR on a 57 year old man, who was conscious and breathing when rangers arrived. He was taken to the Old Faithful Clinic, and then transported by an Air Idaho Rescue helicopter to and admitted to the Eastern Idaho Regional Medical Center in Idaho Falls. His current condition was not available as of late Wednesday morning.
An 18-year-old male patient complained of shortness of breath. He was also taken by ambulance to the Old Faithful Clinic, where we has treated and released.
Six others with minor injuries had gathered next to the building under an overhang to get out of the rain and hail which was coming down at the time.
They had various complaints of shortness of breath, tingling, or numbness. They were all taken to the Old Faithful Clinic where they were treated and released.
A ninth individual walked into the Old Faithful Ranger Station and reported being struck by lightning. This person did not seek medical attention.
Hundreds of visitors witnessed the incident, as they were awaiting the next eruption of the famous geyser.