Born in St. Louis, Missouri, to a wealthy manufacturer of glassware, Drey was a 1935 graduate of John Burroughs School and a 1939 graduate of Antioch College. Drey began acquiring timberland in the Missouri Ozarks for reforestation and conservation in 1951. His holdings, much acquired for the price of back taxes, eventually grew to nearly 160,000 acres (650 km2), the largest private landholding in the state and larger than Missouri's entire state park system. The project, known as Pioneer Forest, is a commercial forest managed in the public interest, with single-tree selection harvesting techniques, which he pioneered. Drey purchased the Greer Mill property in 1987, and later sold it to the Forest Service for incorporation into the Eleven Point District of the Mark Twain National Forest.:12
Drey founded the L-A-D Foundation, which acquires and protects other natural areas in the state, leasing many of them to the state park system at $1 per year. In 2005, Drey was placed at No. 6 on Slate magazine's annual list of the top 60 U.S. philanthropists, thanks to his gift of 146,000 acres (590 km2) of Ozark land, valued at $180 million, to the L-A-D Foundation. Other Drey beneficiaries have included his alma mater Antioch College; John Burroughs School, which uses Drey land for biology and outdoor education courses; the Government Accountability Project; and Missouri Coalition for the Environment, Missouri's first independent citizens' group to address a broad range of environmental issues. In 1991, he donated his papers to the Western Historical Manuscript Collection at the University of Missouri–St. Louis.
His downtown office answering machine message said, "I’m out planting a forest. Please leave your name and number and I’ll try to get back to you before it matures." In 1955, Drey married Kay Kranzberg, who became, like himself, an environmental and civic advocate for more than half a century. Together, they raised three children. Drey died at his home in University City, Missouri at age 98 on May 26, 2015, two weeks after suffering a stroke. His body was donated to the Washington University School of Medicine for science.
- "Timber Baron Preserves Giant Ozarks Forest". NPR. August 24, 2004. Retrieved October 25, 2011.
- Kim Leazenby, Pamela Watson, & Bonnie Stepenoff (May 2004). "National Register of Historic Places Inventory Nomination Form: Greer Mill" (PDF). Missouri Department of Natural Resources. Retrieved 2017-01-01. (includes 4 photographs from 2004)
- MCE. "About Us". moenvironment.org. Retrieved 2016-02-19.
- "Western Historical Manuscript Collection". University of Missouri-St. Louis. Retrieved October 25, 2011.
- Sorkin, Michael D. (28 May 2015). "Leo Drey dies; Missouri's largest private landowner until he gave it all away". St. Louis Post-Dispatch. Retrieved 28 May 2015.
At his office, his answering machine message was: 'I’m out planting a forest. Please leave your name and number and I’ll try to get back to you before it matures.'
- "Leo Drey dies; Missouri's largest private landowner until he gave it all away". 2015-05-27. Retrieved 2015-05-27.