PORTLAND, Maine — 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.

The foundation hopes to announce the first round of grants stemming from the donation later this year, Shafroth said.

Exactly how the money will be utilized remains to be seen, but one of the foundation’s priorities is restoring coral reefs at Biscayne National Park in Florida, Shafroth said, while another priority is the restoration of trout species in western national parks. Those are among the foundation's recent investments.

In addition to funding initiatives that protect fragile ecosystems and species, Shafroth said the money will also be used to create opportunities for young people to visit national parks.

“This grant will allow us to supercharge our efforts to ensure our national parks are for everyone, for generations to come,” he said.

The system's hundreds of units include national parks, memorials, monuments, historic sites and other locations. It includes iconic national parks such as Yellowstone National Park in Montana and Yosemite National Park in California, as well as beloved sites such as the Lincoln Memorial in Washington, D.C. It also includes preserved areas that are less accessible to many people, such as Buck Island Reef National Monument in the U.S. Virgin Islands.

The National Park Foundation is in the midst of its “Campaign for National Parks,” a $1 billion fundraising effort to support parks. Lilly Endowment made the gift to support that effort, said N. Clay Robbins, chair and CEO of Lilly Endowment.

“We believe the National Park Foundation’s campaign will enhance the programming in and promote the future vibrancy of our country’s marvelous system of parks, monuments and historic sites,” Robbins said.