Gwen Casten, 17, died Monday at her family's Downers Grove home, her father's business and police said.
Casten's office stated Gwen died Monday morning. "During this tragic tragedy, the Casten family wants privacy."
Downers Grove police were summoned to Casten's residence at 7 a.m. Monday "for an unconscious 17-year-old girl." First responders found the victim dead.
Casten's office did not reveal death details.
Gwen Casten joined March for Our Lives, according her Twitter profile.
Dawn DeSart named Gwen Casten a "shero" on social media for arranging a shooting-related first-aid training for her high school peers.
Gwen wrote from Downers Grove while getting school updates, and her father from the U.S. Capitol.