A nationwide survey released Wednesday shows a “worrying lack of basic Holocaust knowledge” among adults under 40, including over 1 in 10 respondents who did not recall ever having heard the word “Holocaust” before.

The survey, touted as the first 50-state survey of Holocaust knowledge among millennials and Generation Z, showed that many respondents were unclear about the basic facts of the genocide. Sixty-three percent of those surveyed did not know that 6 million Jews were murdered in the Holocaust, and over half of those thought the death toll was fewer than 2 million. Over 40,000 concentration camps and ghettos were established during World War II, but nearly half of U.S. respondents could not name a single one.

“The most important lesson is that we can’t lose any more time,” said Greg Schneider, executive vice president of the Conference on Jewish Material Claims Against Germany, which commissioned the study. “If we let these trends continue for another generation, the crucial lessons from this terrible part of history could be lost.”

The Holocaust was the state-sponsored mass persecution and murder of millions of people under the Nazi regime and its collaborators. The genocide campaign targeted groups believed by Adolf Hitler’s government to be biologically inferior because of anti-Semitism, homophobia or the like. Using tactics like gas wagons, concentration camps and firing squads, the regime targeted the Jewish people in particular for annihilation and killed nearly 2 of every 3 European Jews by 1945.

The lack of Holocaust knowledge demonstrated in the study is “shocking” and “saddening,” said the Claims Conference, a nonprofit that works to secure material compensation for Holocaust survivors. The survey’s data came from 11,000 interviews across the country, conducted by phone and online with a random, demographically representative sample of respondents ages 18 to 39. It was led by a task force that included Holocaust survivors, historians and experts from museums, educational institutions and nonprofits.