Welwyn

In the 1880s the oil pioneer Charles Pratt began assembling nearly 1,100 acres at Dosoris, in Glen Cove, and by about 1905 several of his children had built houses near the shore. Welwyn belonged to his son Harold Irving Pratt, an oil industrialist, and Harold's wife, Harriet. The house is a large Georgian Revival design overlooking Long Island Sound.

The building history of the house is not settled. The Clio, a history website, dates Welwyn to 1906. The Cultural Landscape Foundation says the Pratts only partly renovated their original 1902 mansion. Wikipedia, citing the museum's online timeline, says the house was designed by Babb, Cook & Willard and renovated in 1920 by Delano & Aldrich. The museum timeline could not be read in this research, so the architects are left open until a primary source confirms them.

The grounds are better documented. The Olmsted firm worked across the Pratt family lands from 1906 to 1909, and Frederick Law Olmsted Jr. analyzed the Pratt holdings in 1908. At Welwyn the Olmsted Brothers laid out the approach drives and service courts and supplied long planting lists, and some of the garden rooms were probably designed by James L. Greenleaf or Martha Brookes Hutcheson. The firm returned in 1934 at the request of Mrs. Harold Pratt. Frances Benjamin Johnston photographed the gardens between about 1914 and 1918, and Samuel H. Gottscho photographed the house in 1933; both sets of photographs are in the Library of Congress, which also holds a Historic American Buildings Survey record of the house.

Harold Pratt died in 1939, and Harriet Pratt lived at Welwyn until her death in 1969. She left the house and grounds to Nassau County, which had no immediate plan for them, and the house stood empty for years. In the 1990s the county sheriff's department used the concrete basements beneath the greenhouses for training. In 1992 the house became the home of the Holocaust Memorial and Tolerance Center of Nassau County, according to The Cultural Landscape Foundation; the Clio entry says a local Holocaust survivor, Boris Chartan, announced the plan to restore the main house in 1993. The center restored the main house, but the greenhouses and formal gardens proved too costly to maintain and were not restored.

Today the mansion holds the center's exhibits and programs, and the rest of the estate is the 204-acre Welwyn Preserve, owned by Nassau County. The preserve has four marked nature trails through a wooded stream valley to freshwater ponds, a salt marsh and the Long Island Sound shore. The museum is open daily for an admission fee, and the trails are open to the public.