People can already visit the 87,000-acre national monument, which has a park service superintendent on the ground and two visitor centers opening today.
The new monument is located east of Baxter State Park and includes the East Branch of the Penobscot River and part of the Maine Woods, where visitors will be able to hike, canoe, hunt, snowmobile, cross-country ski and more.
Burt's Bees co-founder and philanthropist Roxanne Quimby's foundation, Elliotsville Plantation, donated the land and additional funds to the park service with assistance from the National Park Foundation as part of its centennial parks campaign. Quimby is a member of the foundation's board of directors.
The $100 million gift includes the land, which is valued at about $60 million; $20 million to help fund initial park operational needs and infrastructure development; and a pledge of another $20 million of future support, the White House said
"I grew up in this part of Maine," said Lucas St. Clair, Quimby's son and president of her foundation, calling the land sacred to his family.
"To have it designated as a national monument is an incredible moment," he told CNN.
"I look forward to people coming and exploring landscape on their own, and I look forward to these communities that have been really struggling starting to realize some of the economic benefits that national parks can bring," he said.
St. Clair said his mother started buying land in the late 1990s and has been "working incredibly hard for decades" to preserve the land.
Quimby's gift has been debated for years among residents of Maine, where the paper industry once dominated the economy. As with some national park designations in the western United States, many objected to a land transfer to the federal government.
August 25, 2016, marks the 100th anniversary of the creation of the United States' National Park Service, which now oversees 413 sites encompassing more than 84 million acres.