WASHINGTON—Girl Scouts from across the country gathered on the National Mall to celebrate the organization's 100th anniversary with celebrities including Mandy Moore.

Organizers say they expected 200,000 participants Saturday for what would be the largest gathering of Girl Scouts in history. They were hoping to set a Guinness World Record. Girls from every state were expected to attend.

The crowd was also contending with high temperatures. Authorities say dozens were treated for heat-related illnesses, and at least 15 people were taken to hospitals.

The "Girl Scouts Rock the Mall" event featured performers including Erin Willett, a finalist on TV's "The Voice" and "American Idol" finalist Thia Megia.

Other activities included yoga, a fashion show and a news quiz game show from the Newseum.