"It's one of the most special places in the world for him," Richmond said.
Possibly fewer than 5,000 of the Grauer's gorilla survive today in the eastern part of the Congo, where the primates have been threatened by fighting, poaching and illegal mining.
A good census is vital to protecting the apes, said Debby Cox, a primatologist and adviser for the institute.
"Once we have that, we'll know where we need to put our biggest effort for conservation," she said.
The Allen grant also will fund gorilla sanctuaries, and help equip rangers with GPS phones and tablets so they can record gorilla sightings and illegal mines.
"It will make a huge difference," Cox said. "The reality is that without this money, and without gaining the knowledge of where the gorillas are and how to protect them, we could lose this species in the next 10 years."
Since 2008 Allen and his foundation have donated nearly $10 million to African charities and projects like protecting lions in the desert of Namibia and developing a migratory corridor for elephants in Tanzania. They've also contributed to tsetse-fly control in Zambia, drought relief in East Africa and girls' education in Rwanda.
Allen's largest grant, for $3 million, was for a project to analyze scent markers left by wild dogs with the hope of developing chemical mimics that could steer the animals away from human settlements.
The foundation is encouraging ocean research with the Paul G. Allen Ocean Challenge, launched this year to solicit ideas for reducing the impact of ocean acidification. The competition's winner gets $10,000 and a pledge to consider continued funding, Richmond said.
Since 1990, the Allen Foundation has given away $454 million, mostly in the Pacific Northwest. That regional emphasis won't change, said media-relations manager Christina Siderius.
Allen, 60, of Mercer Island is ranked as the 53rd wealthiest person in the world by Forbes with a net worth of $15 billion. He has pledged to give away most of his fortune.
Separate from his foundation, Allen gave $400 million to found the Allen Institute for Brain Science in Seattle. He gave $26 million to the college he attended, Washington State University, for a center to study animal health and diseases that spread from animals to humans.
Allen also owns the NFL Seattle Seahawks and the NBA Portland Trail Blazers.
Information from: The Seattle Times, http://www.seattletimes.com