The 721-acre parcel outside of Rockton in northern Illinois takes its name from a couple who left the group their $439,000 estate.
Natural Land spokeswoman Sue Merchant says retired mail carrier and widower Carl Nygren wanted his assets to be used to buy land. All he wanted in return was a plaque that reads. "To show appreciation of the earth is the most honorable act of humankind."
After Nygren's 1996 death, Natural Land used his estate to help buy the property and started restoring the farmland into prairie, wetlands, hardwood forests and savannas.
Volunteers have planted more than 3,000 trees and more than 1,000 pounds of grass and wildflower seeds.