The official nonprofit organization of the National Park Service is set to receive the largest grant in its history, a $100 million gift the fundraising group described as transformative for the country’s national parks.

The National Park Foundation, which Congress created in the 1960s to support national parks, will receive the donation from Indianapolis-based foundation Lilly Endowment Inc. The park foundation described the gift on Monday as the largest grant in history benefiting U.S. national parks.

The money will be used to address the needs of the country’s more than 400 national park sites, said Will Shafroth, president and CEO of the National Park Foundation.