The newest national park in the Philadelphia region owes its 2013 creation, and its planned expansion, to deals between legacy institutions from two old Brandywine Valley industrial families. And to modern tax incentives.

First State National Historical Park includes colonial sites in four Delaware towns. But its largest property by far is 1,100 acres of woods and creekside meadows east of Brandywine Creek in Chadds Ford Township, Pa., and Brandywine Hundred, Del., plus a planned 270-acre extension on Beaver Valley Road in Concord Township, Delaware County.

Both purchases were made possible by Mt. Cuba Center, the charitable foundation that manages the $300 million-plus family fortune left by the late DuPont Co. chairman Lammot du Pont Copeland and his wife, Pamela.

In 2013 Mt. Cuba paid $20.8 million for the 1,100 acres to Woodlawn Trustees, a group set up by William P. Bancroft, heir to the fabric mills his family started along the Brandywine in 1837.

That's about $19,000 an acre.

The price of conservation has since gone up: Woodlawn and its developer-partners are collecting more than $29,000 an acre for the second purchase, where they had planned houses, and it could be even more because Mt. Cuba's share is not yet publicly known.

Woodlawn isn't a charity, Rodney Lambert, its president and CEO, reminded me. It's a private company that Lambert says follows the social mission set by Bancroft, who died in 1928. It's meant to provide affordable housing in Wilmington and manage land for public recreation up the creek.

Woodlawn rents hundreds of rowhouses on Wilmington's west side, and is building more. Bancroft, who set up Wilmington's city park system (now run by the state), also left Woodlawn thousands of green acres for a "future Wilmington."

Since the founder's death in 1928, Woodlawn and its developer partners have set up affluent residential developments, offices, malls, schools, and churches along U.S. 202 while preserving the green country down to the Brandywine for recreation, with public trails.

Although Woodlawn's website says Woodlawn "donated" the 1,100-acre property for the national park, the land was purchased with millions from Mt. Cuba, the Brandywine Conservancy and the Conservation Fund, and local donors, which raised the cash for the 270-acre addition.

Mt. Cuba's partners paid $8 million to Woodlawn and its partners. Mt. Cuba won't say what it shelled out.

Woodlawn already enjoyed deep property-tax discounts by listing the land under Pennsylvania's agricultural tax-relief program. County records show Woodlawn would have had to pay Garnet Valley schools, the county, and township a total of more than $100,000 a year for four tracts it if it was taxed like other owners; the open-space discount dropped that to below $20,000. As part of the park, the land will be tax-free, said Garnet Valley business manager Christopher Wilson.

Mt. Cuba, based at the 273-acre Copeland family estate and run by a board including the Copelands' three children and three grandchildren who still largely live there, has two related missions, says chairman Amy Copeland Rose.

While Longwood Gardens, run by a different du Pont Family foundation, is known for exotic plants, the Copelands at Mt. Cuba focus on native species. Its garden features three-leafed spring-blooming trilliums with colors so varied they recall Longwood's Orchid Room. Native lady's slipper orchids grow from the knees of tulip poplars, above ponds and streams that the founding Copelands had built. On research plots, plant scientists test native flowers and shrubs.

The garden opened regularly to the public in 2012, and attracted 15,000 paid visitors last year, says executive director Jeff Dowling.

That's less traffic than Longwood sees in a week. But Mt. Cuba's not competing. Chairman Amy Copeland Rose says the grounds and programs build support for preserving what open space remains between Washington and New York and educate visitors for more conscious use of the grounds where they live.

Since 2014 Mt. Cuba has financed the purchase of land and development rights covering more than 20,000 acres in Delaware alone -- an area more than double the size of Philadelphia's Fairmount Park. Since 2005 it has also helped established groups conserve at least 17 other properties in a 100-mile radius.

Ken Hemphill, a retired teacher who heads the Beaver Valley Preservation Alliance, says it's unfair that Mt. Cuba and its allies have had to pay Woodlawn so much for preserving land that Bancroft wanted set aside for just such a purpose. "They haven't done right by society," he told me.

Hemphill notes that Woodlawn still controls more than 500 acres between the park extension and U.S. 202. A Wawa and a WSFS Bank office are already rising on the Delaware end of Beaver Valley Road where Wilmington University plans a campus. "All that land should be part of the national park," Hemphill said.